hunt for bigfoot in code jungle

Moved a web app to be used by all N.A. employees of the client, for unknown reason app was throwing error for 2 employees out of whole population, unfortunately 2 guys are top brace, so we had to figure out the problem asap and i wrote DbTrace component to trace SAP function module calls for specified users and it all seems to be ok and i was out of the scene. Looks like support team was searching for the bug for more than a month and they keep coming back and questioning web app. Today it was found that 2 employee's user defaults are using non US notation and hence SAP was rejecting a valid numeric value 'coz it was expecting in different format, gahhh......