Ahh soz, I can see what's happening, my fault. We always use stored procedures for our report datasets so multivalued parameters get passed as a comma-delimited string (e.g. 'a,b,c').

When you use it in a dataset query like SELECT * FROM dbo.Split(@multivaluedparm, ',') SSRS expands the values out into comma-separated values. ( e.g. 'a', 'b', 'c' ). This is why it is giving the above error.

An easy way to fix this is to convert the parameter results back into a Comma-delimited string. If you open your Dataset properties then go to Parameters and change the Parameter-Value expression to =Join(Parameters!multivaluedparm.Value, ",") . This will combine the parameter values into a single string and pass the to the dataset and function. It will not affect the report parameter itself.

Since img links dont work here I've attached the images showing how to do this or you can use this url for the album: http://imgur.com/a/KRqY8