Try Mercury's CSO. Give them the error number and ask them to clearify the explanation.
Before I could guess at the problem I would need to know more info. Did you get this error every time it tried to call that function? If not was it doing something the other users were not? E.G. took a different path in the script, using different variable, retrieving variables from different locations, using a parameter, etc.
Hope this helps.
Simple minds, Simple thoughts!
I figure if you have the courage to get out of bed in the morning, then how bad can the day be.