If you try to rename (using FTP in Rebug Toolbox) any file (like webftp_server.sprx) stored in flash, you will get an error message and the PS3 will hang. When you reboot, you will be asked to provide a flash drive with a copy of the firmware. It will try to update it and fail (the data is corrupted)
The only fix is going back to 3.55 and then reinstall current rebug. It's a really big bug.
The only fix is going back to 3.55 and then reinstall current rebug. It's a really big bug.