So I have this multi-select:
<label>Select Opportunity Status</label> <br>
<?php
    MultiSelect::create(array(
        'name'=>"OppStatus",
        "placeholder"=>"Select Opportunity Status",
	"dataStore"=>$this->dataStore("oppStatus"),
	"dataBind"=>array(
	    "text"=>"opportunityStatusDesc",
	    "value"=>"opportunityStatusId",
	),
	"attributes"=>array(
	"size"=>5,
    )
));
?>
When I select multiple values, I get this error: 
usp_AgenciesWhoPostedOpportunities('1','3','4', '1', '2017-07-01 00:00:00', '2017-07-31 00:00:00');
The proc is expecting these params:
usp_AgenciesWhoPostedOpportunities(IN OppStatus char, IN OrgStatus char, IN StartDate, IN EndDate   datetime)
In the error, I selected three items from the multi-select. As you can see, it added 1, 3 and 4 to the params list. I expected it to call the proc like this: usp_AgenciesWhoPostedOpportunities('1,3,4', '1', '2017-07-01 00:00:00', '2017-07-31 00:00:00');
Notice how the first param is a list of the IDs