Happend a couple of times, this time i performed a stealth kill.
I could not fire or scope in or anything other than

Shield/Stealth and sprint/jump.

ye had that aswell only two or three times in 20+ hours though

This happened to me the other day on lighthouse. I could still run jump cloak and armor, however I could not switch weapons, pull out my grenade, or melee. Really weird, it seems the only way to get out of this is to die =[
I ran away from the fighting to see if maybe there was a way to undo it (sliding while cloaked? nope.), but to no avail.
Oh well, add it to the list of bugs-to-be-fixed.
Fingers crossed everyone!

Yeah i had this problem a couple times on MP but it seemed to only come up when the lag was really bad, so maybe it's lag related

I have this happen occasionally, right in the middle of firing at someone it will just stop and I usually die before I can start firing again. I assume it's due to lag, but maybe not...

Wow I wondered if others had this problem , this ruined my killstreak mannn. It svcked but I was able to switch to my pistol but still wasn't able to shoot or reload. Blah

Happened to me in campaign too just once though, not in multiplayer yet. Your gun doesn't appear too right?