You have to define the data type for the parameters ([Forms]![frmRptTrafficReport]![CurrentYear]) for the query. Here's a link to the article I found http://www.fontstuff.com/access/acctut01.htm when I had the same problem. Here's what my query ended up looking like:

PARAMETERS [Forms]![CdrlForm]![RptMo] Text (3), [Forms]![CdrlForm]![RptYear] Short;
TRANSFORM Count(ClinMatch.InFile) AS CountOfInFile
SELECT ClinMatch.clin
FROM ClinMatch
WHERE (((ClinMatch.CalMo)=[Forms]![CdrlForm]![RptMo]) AND ((ClinMatch.CalYr)=[Forms]![CdrlForm]![RptYear]))
GROUP BY ClinMatch.clin
PIVOT ClinMatch.File;