Filter - multi-select ISSUE after migrating to R4.1

Experts,

We recently migrated from R2 to R4 and one of our most important Universes has a multi-select filter pre-defined as such when you look at it with the Information Design Tool:

USER_DT.MTH IN (@Prompt('Enter as of Months', 'A',,multi,))

The syntax Parses just fine. But when I try to use it in a simple query with Webi 4.1 it is only successful when I enter 1 month. If we enter more than 1 month it throws this error:

Database Error: [Microsoft][ODBC SQL Server Driver][SQL Server]Statements could not be prepared .. (IES 10901) (WIS 10901)

It's interesting because when you look at the SQL syntax from webi it writes it correctly using the 'IN' clause.

Any thoughts or direction?

thanks,

Matt