I've been having this error in my game recently where some creatures who use the NPC/Player animations (dremora, skeletons) will try to run toward me but instead they will just move their upper body with weapons drawn but they remain stationary with their lower body unanimated. The only animation mod I have active that I know of is Antares.

Here's my excruciatingly long list of mods....

[Game Files]GameFile0=abotWaterLife.esmGameFile1=Assassins Armory.esmGameFile2=Better Heads Bloodmoon addon.esmGameFile3=Better Heads Tribunal addon.esmGameFile4=Better Heads.esmGameFile5=Bloodmoon.esmGameFile6=Book Rotate.esmGameFile7=GDR_MasterFile.esmGameFile8=H.E.L.L.U.V.A._Merchant_Containers.esmGameFile9=Hilgya the Seamstress.esmGameFile10=Morrowind Advanced.esmGameFile11=Morrowind Patch v1.6.5-BETA.esmGameFile12=Morrowind.esmGameFile13=MW_Children_1_0.esmGameFile14=Rise of House Telvanni.esmGameFile15=The Undead.esmGameFile16=Tribunal.esmGameFile17=TR_Data.esmGameFile18=TR_Mainland.esmGameFile19=A Call to Issilar.espGameFile20=abotWaterLifeTRaddon.espGameFile21=abotWhereAreAllBirdsGoing.espGameFile22=AEA-Compatibility.espGameFile23=Alakazar's Lamp.espGameFile24=Animated Morrowind 1.0.espGameFile25=Antares' Big Mod 5.espGameFile26=Apostates of Oblivion_2.1.espGameFile27=Ashes.espGameFile28=Assassins Armory - Patches.ESPGameFile29=Atronach Expansion X.ESPGameFile30=Avenge Your Death!.espGameFile31=AYD Spells.espGameFile32=BB Dark Brotherhood by Westly.espGameFile33=BB_Grimoires.espGameFile34=Better Bodies.espGameFile35=Better Clothes_v1.1.espGameFile36=Better Skulls.ESPGameFile37=Better Telekinesis.espGameFile38=Birthsigns.espGameFile39=BirthsignsAMFun_BM.espGameFile40=Book Additions.ESPGameFile41=Book Rotate and Jackets.ESPGameFile42=Books of Vvardenfell_2.0.espGameFile43=Brittlewind fix.espGameFile44=Building Up Uvirith's Legacy1.1.ESPGameFile45=Census and Excise Office.espGameFile46=Class Abilities 3.1.espGameFile47=Clean Board Games.espGameFile48=Clean chapelsv2.espGameFile49=Clean Collectible cards.espGameFile50=Clean Hold it-replacer.espGameFile51=Clean New Seyda Neen 1.5.espGameFile52=Clean Official Plugins v1.1.espGameFile53=Clean Staff Agency1pt0.espGameFile54=Clean To Serve Sithis_.espGameFile55=Clean Ungen 1.7.espGameFile56=CM_Minor_Quests_1.2.espGameFile57=ColovianFurGauntlets-BM.espGameFile58=Complete Armor Joints.espGameFile59=Constant Effect Additions.ESPGameFile60=CR Gnisis Expanded 1.0.espGameFile61=Creatures.espGameFile62=Dagger of Symmachus.espGameFile63=DagonFel_Well.espGameFile64=Death's Doorstep.espGameFile65=Detect Owner.espGameFile66=Deus Ex Machina.espGameFile67=DN-GDRv1.espGameFile68=Dwemer Sentinel.espGameFile69=DX_CreatureAdditionsV1.0.espGameFile70=DX_Thedungeon.espGameFile71=DX_WereCrocs!.espGameFile72=EmmasTowns.ESPGameFile73=Enhanced Detection.espGameFile74=Enhanced Summoning.espGameFile75=equimanthrone.espGameFile76=Exotic Imports by Westly.espGameFile77=Fair Magicka Regen (one Percent).espGameFile78=Fast Eddie Fix v .0001.espGameFile79=Fligg's Slave Mod.espGameFile80=Fliggerty's Almanac.espGameFile81=Fliggerty's Fleeing Fetchers.espGameFile82=Galsiahs Character Development.espGameFile83=GCD Over 60 level speedup.espGameFile84=GCD Restore Potions Fix.espGameFile85=GCD settings fairly easy.espGameFile86=GCD StartScript for Trib or Bloodmoon.espGameFile87=GCD_SS_patch.espGameFile88=GDR09_Aleft.ESPGameFile89=Gladiator.espGameFile90=Go To Jail 3.5 - T B.espGameFile91=Goblin Race.espGameFile92=Gondoliers.espGameFile93=Greater Undead.espGameFile94=Grow Towers [Final].espGameFile95=H.E.L.L.U.V.A. Mod.ESPGameFile96=Hairs by Mandamus & Kalian.ESPGameFile97=Hilgya the Seamstress Expansion 1.espGameFile98=Hold it - SF npc addon.espGameFile99=Hold it-COM addon.ESPGameFile100=House of Mannequins - Mistform fix.espGameFile101=House of Mannequins v1.0.espGameFile102=Ice Siren.espGameFile103=IceNioLivRobeReplacerPLUS.espGameFile104=Illuminated Order v1.0 - Bloodmoon Compatibility Extras.espGameFile105=Illuminated Order v1.0.espGameFile106=indybank.espGameFile107=Keyring.espGameFile108=LeveledMagicka.espGameFile109=LGNPC Master File.ESPGameFile110=Lich Father Act I & II.ESPGameFile111=Lights_300_V4.espGameFile112=LOCH_Seamless_BB_Ayleid_Race.espGameFile113=Lothavor's Legacy BB addon.espGameFile114=Lothavor's Legacy.espGameFile115=Mashed Lists.espGameFile116=MDP - Full.ESPGameFile117=MD_Azurian Isles.espGameFile118=MD_Kione_Hairstyles.ESPGameFile119=Mindflayers.espGameFile120=Mod Logbook.ESPGameFile121=Mournhold Expanded COM NC.espGameFile122=MTC-CoM.espGameFile123=MW_Adv_Required.espGameFile124=MW_Public_Library.espGameFile125=Neo's Unique Creatures.espGameFile126=New Argonian Bodies - Clean.espGameFile127=New Gnaar Mok COM Patch.ESPGameFile128=New Gnaar Mok.ESPGameFile129=New Khajiit Bodies - Clean.espGameFile130=New Khajiit Diversity(BEAST).espGameFile131=New Veloth's Judgement.espGameFile132=Nirnroot.espGameFile133=NX9_Guards_Complete.ESPGameFile134=Oread Race.espGameFile135=OR_DaeRaceBETA.espGameFile136=Particle Arrow Replacer.espGameFile137=Pearls Enhanced - Colored Pearls Add-on.ESPGameFile138=Pegasus Equipment.espGameFile139=Persuasion Response Expansion.espGameFile140=Psy_VGR_Armour.espGameFile141=RAMF_for_NPCs.espGameFile142=RD_wands.espGameFile143=Redaynia Village.espGameFile144=Reign of Fire v1.92BETA [Razhkul, Rev. Gluby].espGameFile145=Reign of Fire White Dragon and Dungeon [bbslayer_07].espGameFile146=RoHT GDR Aleft Patch.espGameFile147=Scripted_Spells.espGameFile148=Seamless_BB_Falmer_Race.espGameFile149=Seraphs - Water.espGameFile150=Sheogorath's Crucible of Chaos.espGameFile151=Silt Strider Armor - Ashlander Guards.ESPGameFile152=Silt_Striders_Are_In_Vvardenfell.espGameFile153=sm_Ayleid_Extras_3.3.espGameFile154=sm_creatures_01.espGameFile155=sm_creatures_02.espGameFile156=sm_DwemerStaves.espGameFile157=sm_goblinshman.espGameFile158=sm_summonexpanded.espGameFile159=Sris_Alchemy_BM.espGameFile160=Star Boi's Epic Armory.espGameFile161=Starfires NPC Additions ver-1.11.espGameFile162=Teleportation Spells.espGameFile163=The Battlespire v1.1.espGameFile164=The Neverhalls.espGameFile165=The Shrine of Mephala by Westly.espGameFile166=The Tribe Unmourned (GHD).espGameFile167=THE_UNDERGROUND_2.espGameFile168=Thieves Guild Fences.espGameFile169=To The Death.espGameFile170=TR_Map3v.76.espGameFile171=TR_Map4v.58.espGameFile172=TR_Map5v.12.espGameFile173=TR_Map6v.07.espGameFile174=TVwofs.espGameFile175=UG2PhaseC_v06.espGameFile176=ULM Death Pass.espGameFile177=Undeads - Skeletons Arise from Death II.espGameFile178=Undeads arise from death 1.5.espGameFile179=Undeads Skeletons Arise from Death.espGameFile180=Unique Jewelry and Accessories.espGameFile181=UniqueFinery.espGameFile182=Uvirith's Legacy Book Jackets Add-on.espGameFile183=Uvirith's Legacy_BETA1.09.espGameFile184=Vality's Ascadian Isles Addon.espGameFile185=Vality's Bitter Coast Addon.espGameFile186=Visceral Discernment.espGameFile187=Vivec Expansion 2.0.espGameFile188=Vivec's Fate.espGameFile189=Westly Presents-Dremora Markynaz.espGameFile190=Westly's Master Headpack X.espGameFile191=Westly's Races.ESPGameFile192=Westly_Presents_BB_Almalexia_Add_on.espGameFile193=Westly_Presents_Tang Mo_People of the Waters.espGameFile194=wl_dockclutter.esp

Do you use LizTail's Animation Kit?
This is a common problem when using it, but you just have to open the Kit and click the button that updates all your animations. (can't recall the exact name of the button)

Click the "Fix Animation Errors" button. That should do it.

(if you're using LizTail's animation kit, that is)

Yes I do, I clicked it. I'll test it later to make sure it worked but I'm sure it did, thanks guys

If that doesn't fix the problem, reinstall the animation files.

If it does, please post your results. I was having the same problem testing a new male animation. Glued all the bipedal creatures to the ground.

If 'Fix Animation Errors' doesn't work then press 'Rerun Setup' (or something like that).
Either of those two have always been able to resolve this issue for me.

A last resort, as Jac said, is to reinstall the base_anim files.

"Fix Animation Errors" button fixed the issue right away. Thanks guys!