Trouble passing lookup to a new entity form.

I'm having an issue with the openEntityForm javascript call. I'm getting an error and can't figure out what I'm doing wrong.

function Submit() {
var parameters = {};
parameters["tdn_requester"] = Xrm.Page.context.getUserId();
parameters["tdn_requestername"] = Xrm.Page.context.getUserName();
parameters["tdn_requestertype"] = "systemuser";
Xrm.Utility.openEntityForm("tdn_goldstarreport", null, parameters);
}

This results in the following error. 

System.InvalidOperationException: CRM Parameter Filter - Invalid parameter 'tdn_requestertype=systemuser' in Request.QueryString