Can't copy files from 2003 to 3.51

We have 2000 Servers, one 2003 Server, NT4 Server and one old 3.51 Server.

It would seem because of a recent patch that we can't copy from the 2003 to
the 3.51.

I can copy from the 3.51 to the 2003, and back and forth between all the
others - but not from the 2003 to the 3.51.

It gives this error;

Error copying file or folder.
Cannot copy 'file': The parameter is incorrect.

Any suggestions please?

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Regards,

Slarty Bartfast