Error 56 is "Attempt to run uncompiled expression asdfasdf"

The Webservice in question has a parameter Number nBatchIdNum

I am upgrading it from 17.0 to 18.2 and making some changes to it.

My first test is I key in a stupid BatchIdNum like asdfasdf and it pops up with error 56.

I then change the parameter to be a string and do a Move (Number(sBatchIdNum)) to nBatchIdNum

Same error, this time on the Move (Number ... line.

Is there some generally accepted way of trapping stupid Web Service parameter values and nicely passing back a readable error message?

Thanks
RChi