There's a limitation in the current version of QuickTime 7 which restricts any file name plus extension to 63 characters or less.

The full path may still be MAX_PATH (see WINDEF.H) characters long, but the file name must be 63 characters or less.

This limitation should be relaxed in a future version of QuickTime.

Also, the text encoding of the pathname passed to NativePathNameToFSSpec must match the system code page of the Windows system. This means you cannot use Unicode pathnames (either UTF-8 or UTF-16) with this function.

I suppose it is not a problem of Soundtaxi. Try to rename files according to the above mentioned limitations and then remove DRM from them.