Ok , problem solved after reboot all back to normal. The FAT card is my 2nd card with all pnds not Slackware (ext2) and when I tried to delete a file I got the Info " not allowed , file system is read-only". So all is ok now, but how could this come ?
Run a chkdsk or fdisk. That occurs when Linux encounters an error (any error) on a FAT file system. Rather than risk screwing up the disk further it just makes it read-only. It's almost certainly a single file or directory that's causing the problem, like one PND has gotten corrupted or something.
Yeah, the only way to make FAT32 files read-only is to mount the filesystem as such. Next time it happens, you should check dmesg|grep mount for clues. An FS issue could cause this, but it normally wouldn't go away by rebooting. I bet the wrong mount script got executed or someting.