Relational Currency Code NAV - 5.0

I am having a problem posting intercompany transactions because some how the relational currency code on the change exchange rate card has been changed from USD to another number which does not exist in the other company. At this time multiple currencies are not being used, so there is no curreny code being used. Can someone please tell me how to cahnge it back to the original setting.

P.S.: I have also looked at a copy of my existing test database (which gets updated monthly) and the relational currency code listed is USD.