Thanks to bug reports from users of little endian machines, I was able to isolate the issue where MyPasswordSafe might have trouble loading an existing keychain.
I’ve patched it up to read and write little-endian files natively, so you should have no issues utilizing existing keys with other systems – please note that this means any keys created with my initial port of MyPasswordSafe are now incompatible!
You can download the updated version from my software page.