Date Conversion Stored Procedure working on SQL 2008 but not on SQL 2005

Date Conversion Stored Procedure working on SQL 2008 but not on SQL 2005 We have a very short Stored Procedure written and working fine on SQL 2008. Same stored Procedure is not working in SQL 2005. We need a coder to be able to make it work in SQL 2005 The Stored Procedure is: datediff(d,"VWTrucks"."BAFDate",convert(datetime,left("VWTrucks"."ReferenceNum",6)+'01')-1) as NoOfDaysDiff,