There are a few things you could try.
Firstly - have you patched your game fully? It might have been a bug in earlier versions of NwN, so patching is always a good idea. The current patch is version 1.62, and I'd advice you to do this before trying much else.
If you have a save game from before you hand in the last one, then patch and run that game, and see if the problem persists.
Secondly, after you have patched and this problem persists, - it is possible to spawn items into the game. If you are 100% sure (or 110) that you have handed in all the tomes, you could try to spawn in the tomes again, to see what tome(s) Eltoora still wants.
The way to spawn in items is to use the dm/console commands.
The easiet way to do this is to type in your chat-box (the small box labled "Talk:" just above your quickslots.)
Type:
##DebugMode 1 (note the ##, and this is case sensitive, so capital D and M).
next type:
##dm_spawnitem <itemtag>
the itemtags for the tomes should be (I've only tested one of them, so let me know if some are wrong, and I'll find them again, or you can do it yourself, if you wish, via the toolset, and chapter 2 module).
m2q01timaskdeath
m2q01timaskfire
m2q01timaskice
m2q01timasklife
m2q01timaskreson
You can read from the tagname which tome it is (deat, fire, ice etc).
The spawncommand spawns in the item where your mousecursor is located, so be carefull not to place the mouse outside the gamearea or inside a wall
after you have spawned in with the dm_spawnitem the tomes you whish, exit the debugmode by typing
##DebugMode 0 (again - case sensitive command).
Then you should have the tomes you whished again, and you can try handing them in again and seeing if this triggers the end of the quest.
If it dosen't (and you have patched), then I'm affraid I can't really help you more.
But try patching first (if you haven't).