Looks like the problem is in your latest save, unfortunately (a problem with the game files could be fixed by simply re-installing it).
If you backup your saves, and then make a copy of your latest and newest working save folders, you can determine which file(s) became corrupt by copying files from the copy of the most recent working save into the copy of your latest save. I'd start with the inventory files (items.000 and inv.*). Once the copy of the latest starts working properly, you know which files are the problem (though you may have to create a new copy of the latest save folder and repeat the process to make sure you isolate only the problem files).
Mixing files between different games, or from an older save in the same game, can cause minor to major problems, depending on the file(s) in question. For example, the items.000 file keeps track of random stats on equipment; replacing it would likely mess up most or all of your equipment. World.* files keep track of the environment and items left directly on the ground; it would be relatively painless to delete a world file and have the game replace it with the default version the next time the save was loaded (that would re-seal quest opened locations and possibly eliminate quest items), but there are different world files for Rivertown, Verdistis and the Dark Forest, so it would be highly unlikely you would have the same problem in each.
Check your messages (click 'My Stuff' in the top menu bar, then 'My Messages').
