It sounds like your saved game files may be corrupted. Corruption can occur due to file fragmentation, such can be caused by constantly over-writing the same saved files, and is why it is recommended in the game that you save often and in different slots. Once corrupted, by this or other means, re-installing the game will not necessarily fix a corrupted saved game file as the saved game is what contains the module information being addressed.
Something else that can cause corruption is not having enough free disk space available on your hard drive. You need to maintain at least 15 GB of free disk space for NWN 2 (and MotB) and at least 20 GB with NWN 2 plus both expansions.
By way of explaining NWN DM's question for you... If, at some point, you happened to have opened the game module in the toolset, whether or not you actually did noting more than look around a little, that would be enough to cause corruption since, by default, the toolset auto-saves the module file every 5 minutes and those saves would be identified as a different version, even though you may not have manually saved the file.
As a test, rename your NWN 2 folder in Documents (My Documents) and start the game with a new character, play through the first conversation, save the game (manually do not use quick save), This will fully create a new NWN 2 folder in Documents. Next, copy your saved game from the original folder you re-named into the newly created folder and try that saved game and see if if that fixes the problem. If it does, it means that something in your original folder may be corrupted.