Try ...
SELECT tblData.[No], tblData.Client, tblData.ClientNo, tblData.Address, tblData.Date
FROM tblData
WHERE (((tblData.Client) Like "*" & [Forms]![frmSearch]![txtSearchString] & "*") AND ((tblData.Requested) Like "*" & [Forms]![frmSearch]![cboYear] & "*"))
I made the bit in red...