Excel “GWXLUS.XLA” ERROR

PII 500 128MB Ram/Newer Machine:When I hit the little disk button on the toolbar to save a file, I get this error: “GWXLUS.XLA not found,unable to save.I am able to save files just fine when I go to “Save As” though.If you have seen this error or know what it is please help.Thanks in advance.Also,if you know of a good Excel troubleshooting webpage please send it.I cannot find this error at Microsoft’s.