Hi Nova227,
The manuals of Genos and SX models state that a maximum of 2500 files can be stored "per folder". However, I assume that this number applies to a folder
including all its subfolders.
Basically, I recommend only copying the files to the User drive that you actually need/use, i.e. not entire collections with thousands / tens of thousands of files. Why don't you just work with USB sticks?
By the way, with the internal Backup function you will always have problems like this if you have a lot of files in User drive. In addition, the only thing you can do with a .bup Backup file is to restore the complete system settings it contains, including the content of the user drive, to your (or another) SX900 (however, the current content of the User drive will be overwritten!). As is well known, it is not possible to extract/copy individual files from a .bup file.
My recommendation: FORGET the internal Backup function! Simply back up the internal user-defined system settings regularly by saving the "System", "MIDI" and "User Effect" Setup Files to a USB stick (in "Menu > Utility > Factory Reset/Backup") . Then copy these files to the computer as well.
As long as you don't edit the files in the User drive, you don't need to backup them, since you still have the original files on the computer and/or USB sticks anyway. If you edit or create a file in the SX900's User drive, save/copy it to a USB stick as well (copy these edited files to the computer regularly as well), and everything is fine.
Best regards,
Chris