Unicode character mapping problem

I am migrating from NT 4 to NetWare 5.1 File & Print.

On my existing NT4 environment, I have many office documents created and named using Japanese characters. Although some will copy fine to the NetWare server, others produce the following errormessage:

Cannot copy “filename”: No mapping for the Unicode character exists in the target multi-byte code page.

Novell say that I need to use the Japanese version of NetWare, which is not practical as 95% of my users are English and administration needs to be done in English. Any suggestions on how I can make my English version of NetWare support these files?