[AccessD] MonthName Function Undefined - What's Missing?:

To all,

I installed an A2K app at a remote customer site and found that the
expression 'Time Period: MonthName([Period_Start_Date],True)' in one of my
queries raises the error 'Undefined Function MonthName in Expression'.  I am
told it was a full blown install of A2K, but something appears to be
missing.

Any ideas?
TIA, as always,
Ron