I recall there being a known bug related to exchange of the EEC stock certificate... in any case, when I speak with Carnius and click the "stock certificate" option, he only offers to tell me the value, and never actually offers to buy it from me. Anyone remember the fix?

Must be due to a mod. In an unmodded game, the only dialogue in which Carnius will tell you the value of the stock certificate also has the option to turn it in.

Anyway, the known bug occurs when you try to turn it in at its maximum value of 12000. This can trigger a CTD.

My only mods are:

GameFile0=Bloodmoon.esm
GameFile1=Morrowind Patch v1.6.4.esm
GameFile2=Morrowind.esm
GameFile3=Tribunal.esm
GameFile4=adamantiumarmor.esp
GameFile5=AreaEffectArrows.esp
GameFile6=bcsounds.esp
GameFile7=EBQ_Artifact.esp
GameFile8=entertainers.esp
GameFile9=LeFemmArmor.esp
GameFile10=master_index.esp
GameFile11=Siege at Firemoth.esp

Plus MCP 1.6

Yep, broken by Morrowind Patch 1.6.4. The patch makes a typo in Carnius' dialogue that prevents all the choices from being displayed.

If you side with Falco, you can turn in your certificate to Constans after Carnius is out of the game.

Thread moved to Morrowind Mods, since this is a mod issue.

Well, thanks for the quick work, guys. Sure enough, soon as I finished the EEC quests and Carnius was dead, his assistant pony'd up.

Those dialog typos are supposedly fixed by http://www.gamesas.com/bgsforums/index.php?showtopic=1041190.