Yesterday, I installed PortableApps and somes portables applications on a 2 GB USB key. Everything seems to work fine.
Today, when I plug in the USB key, Windows 7 asks to format it.
So, I format it (FAT32), reinstall everything and check it again. Everything worked fine. Then, I remove the USB key using the eject button in PortableApps menu and plug it in again. Once more, Windows asks to format the key.
I checked in Window's Computer Management and find out filesystem changed from FAT32 to RAW.
What's the problem?