Try This:

Reformat your 320 HDD. Because the Slim is a highly redesigned unit in terms of architecture the HDD may have problems recognizing certain elements of the console. People will say this shouldn't happen; I completely agree with that statement.

If reformatting is not an option, stop complaining to the people in a forum and call the guys who actually build the thing. Sony.

Call Sony and ask them, it's probably faster and easier then asking the same "why is does 320 work on fat not slim" over the forums for 2 weeks.

I apologize if this was already suggested or if the issue had been sufficiently been resolved; I skipped a lot of the junk that was posted.

-Scrubs