Hi - I believe you have misunderstood my post above. What you seem to be describing is adding FX RATES to the Exchange tables - my post above describes a once off set up step that is required - adding rate TYPES to the FX tables.
If it is only happening with one creditor - then the Rate Type assigned to this creditor is different from the other creditors. Open a creditor that works - click on the Options button and check what Rate Type is assigned to this creditor. Then you could assign the same Rate Type to the problem creditor. This should resolve the problem - and you probably have security rights to edit a Creditor record so you won't need administrator help?
If you don't have security rights - then you will need an administrators help with this. Either change this one creditors rate type...or change the set up as per my original post so that all potential Rate Types will work.
Best regards,
Ian.