Trying to run the sample Cognos 10.1.1 report, "Overdue Work Orders By Location" on SQL Server, the following error occurs:
The operation "_add_days" is invalid for the following combination of data types: "nvarchar" and "integer".
Using the incorrect MS SQL Server ODBC Driver.
Resolving the problem
When creating your Data Source in Cognos Administration, make sure you specify the correct driver.
MS SQL Server ODBC driver has two versions. When creating the DSN, you should pick "SQL Server Native Client xx.xx" ( SQLNCLIxx.DLL ), not SQL Server (SQLSRV32.DLL).