Reporting Procedure Where Clause Help (Multiselect)

I realise this may not be a suitable solution for your environment but by far the easiest thing to do is use Query Type = Text when creating the SSRS dataset and pasting the query in directly.

This way you can just write

SELECT
Col1,
Col2,
Col3
FROM
YourTable
WHERE
YourFilterColumn IN (@SSRSParamater)

and SSRS will handle expanding the parameter

Some more details if you really need to get it working with a stored procedure: http://ift.tt/1nm0AUT