Add parameter

Newbie here!  

I am trying to modify an existing report  to allow the user to enter multiple user id's to a report.  Currently, the report will allow you to filter by one user id, but I need to have it filter by more than 1.  I changed the parameter to 'allow multiple values'.  I then changed the query to IN(@parameter) instead of =@parameter. Now when I attempt to run the report I get "The report parameter has a defaultvalue or a validvalue that that depends on the report parameter.  I changed the order of the parameters and still get this error.  My report consists of open Purchase Orders.  It originally was set up to enter in a buyer id.  After that was established then it would allow you to select what supplier id(s) you wanted to filter by.  I am doing all of the editing in Visual Studio 2012, then it gets deployed and ran on Report Manager.
Copy-of-Expedite-Report-by-Buyer.rdl
Expedite-Report-by-Buyer.rdl