Sony has announced in their official blog (http://blog.us.playstation.com/2008/10/21/psp-playstation-portable-v501-update/) that their new PSP firmware is coming very soon.
The new PSP firmware fixes a bug in version 5.00 which affected the Memory Stick Duo. Version 5.00 was only released this time last week.
8GB and 16GB versions of Sony’s proprietary storage cards were not being read properly by the PSP and telling users that there wasn’t enough free space to store downloaded files into PSP even though enough space was in fact available. According to Sony this firmware update will fix the problem.