Passing BOUSER into a SQL Server function

Hi all,

I wish to pass the BOUSER variable into my SQL function which returns a 2 column table when it is executed. The SQL I have in a derived table is this.

SELECT UserID, UserGroupID

FROM   fnRptUserGroupSecurity(@Variable('BOUSER'))

However when I validate this SQL in the derived table I get this error message from SQL Server 2014

[Microsoft][SQL Server Native Client 11.0][SQL Server]Conversion failed when converting from a character string to uniqueidentifier.

The UserID column is of type UNIQUEIDENTIFIER and the parameter that is passed in to the function is of type CHAR(36).

Any ideas about how I can get around this error message in IDT as until it is validated I cannot see the columns in the dervied table to be able to join on them in the .dfx?

Thanks,

Christian