I had this problem too. Turns out that once an item ends up in your inventory overflow when you put it into your regular inventory you have to re-zone or log to make it valid again.
Happens alot if you carry too much stuff like me. :-(
Yup i had same prob but couldnt fix it with moving stuff but then again i guess i didnt try logging. I should have tried that before asking a gm and getting nowhere.