If it was out of memory, you wolud get an error message whn you save. Max 99 files in the root directory, and 256 files in a folder.

Are you using the Freeze function?
Did you check the Registration Memory Contents page?

If this doesn't help you may want to call us...
714.522.9000

Yamaha USA Support
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Yamaha Customer Support
www.yamaha.com/pacsupport
714.522.9000