Did you load these files before the update? They may just be corrupt from the onset. If you load a backup right after backing up your keyboard - you can test the backup and there's nothing lost. Just for kicks you can [STORE] a change to a user Performance and make sure after you restore the backup that the change is reverted back.

An "illegal file" type of issue would jump out fairly quickly.

If you wanted to go even further, you'd copy the X7A file from your USB stick transferred from Montage (copy it to your computer's hard disk). Then copy this file back to your USB stick with a different name (testfile.X7A) - then load "testfile.X7A" on your Montage. This will test to validate that the version saved on your hard disk is good. And no corruption happened from USB to Hard Disk or from Hard Disk back to USB. This dance will give confidence that backups of the backup files (X7A files) on your computer hard disk will be good.

That, at least, covers corruption. I guess it's not established if your file is corrupted or not - or if there's some loading issue in v3.5. I don't think there is, generally, a backup file loading issue since others seem to have restored pre-3.5 backups fine. But perhaps not all permutations (FW version used to create X7A file, data on X7A, etc) were tried or expressed in the forum.

On the onset - I think one would approach this as a bad file assumed until proven otherwise. Given a reverted version doesn't load the file - it seems to suggest the file itself is bad.

What's the file size of the X7A you're loading?

I did.nt load the files before update.............i will try directly after the next backup.
I was pleased that i make a USER save from all the set list performances in the "LIVE" banks.........so i stell have all the sounds and most of the settings.
Backup file size is 335 MB...............
I'll go and try the saving on de hard disk en recover with a different name.........i'll let you know..............thans Jason!

335 MB eliminates the zero-size issue one can see. Seems like a reasonable enough size although not entirely conclusive (can't tell health of a file by it's size if it's over a certain amount).

It is recommended that you use USB Flash Memory device (USB stick)
A File with the extension .X7A is the only Type that can be restored as a Backup File.

From the Owner’s Manual:
[b)[USB TO DEVICE] terminal
Used to connect this instrument to a USB flash memory device. This lets you save data created on this instrument to an external USB flash memory device and load data from a USB flash memory device to the instrument. Save/Load operations can be performed: [UTILITY] —> [Contents] —>[Store/Save] or [Load].
NOTE:
• Only USB flash memory devices can be recognized by this instrument. No other USB devices (such as a hard disk drive, CD-ROM drive and USB hub) can be used.
• The instrument supports the USB 1.1 to 3.0 standard. However, note that the transfer speed differs depending on the data type and the condition of this instrument.

The instrument supports the USB 1.1 to 3.0 standard

This information is counter to earlier discussion from Yamaha. The earlier discussion described the USB TO DEVICE port as USB 2.0 maximum (USB "high speed" ) and not capable of USB 3.0 speeds (USB "SuperSpeed" ). And also that the port is not capable of the newer power sourcing specification available in USB3.0. USB3 is designed to be backwards capable with USB2 - so USB 3 should be backwards compatible with USB 2.0 host controllers. However, the fact that USB3 can plug into a USB2 port is different from saying the instrument supports the USB 3.0 standard - because the USB 3.0 standard implies many more items beyond what USB2 can do.

@ Bad Mister and Jason, thanks for your messages, i had two backup files that both were damaged, the exact reason is unknown, i bought a new USB stick (the same model and brand) and formatted this on the Montage (the first usb sticks were formatted on a computer).
Than i made a new backup en loaded this for testing, no problems happened.
Now i have 3 different USB sticks, one for updating, one for backup and one for users, library, wave file etc. etc.
Everything works fine now, thanks again.