If the cookie is the only thing returned, there won't be a recordset like there is with a SELECT query. I think you have to use the parameterized query in this situation.
I have never used the {call procedure(?,?)} format. I only use the name of the SP as the query. This is documented in the help file that way. And I also create the parameters as shown here, rather than using the SET function. This is a bit cleaner IMHO and it's really easy to add another parameter if necessary.
What happens if you use string for the cookie value? VARBINARY does not correlate to any datatype in LabVIEW so I would try string format.
Since this procedure belongs to the master database, you may have to set your default catalog to master (in connection settings). I've never had to call a system SP to know for sure. Maybe the server automatically recognizes it as a system SP.