Thanks.  Here is the code in it's entirety.
Note there are 3 places where the WHERECLAUSE is failing.
This code was COPY/PASTED from another program of mine that works fine and
appropraite changes were made.
I have gotten around this by implementing code in the FORMAT event on the
detail section of the report, but I don't like doing it that way.

Private Sub btnPreview_Click()
 Dim stDocName As String
 Dim iMonth As Integer
 Dim iYear As Integer
 Dim iWork As Integer
 Dim strg1 As String

 On Error GoTo Err_btnPreview_Click

 WhereClause = ""
 Select Case Frame0.Value
   Case 1
     stDocName = "Labels Current Members"
   Case 2
     stDocName = "Renewal Labels"
     iMonth = Month(txtDate.Value)
     iYear = Year(txtDate.Value)
     iWork = iMonth + (12 * iYear)
     WhereClause = "ABS(" & Str(iWork) & " - GrossMonths) <= 1"
   Case 3
     stDocName = "Labels Current Members"
     WhereClause = "ShortName = '" & cmbCategory.Value & "'"
   Case 4
     If IsNothing(cmbGroup.Value) Then
       MsgBox "Please enter a GROUP name"
       Exit Sub
     End If
     stDocName = "GroupDonationsSummary"
     WhereClause = "StartDate <= #" & txtDate.Value
     WhereClause = WhereClause & "# AND ((EndDate IS NULL) OR (EndDate >=
#" & txtDate.Value & "#))"
 End Select
 'MsgBox WhereClause
 DoCmd.OpenReport stDocName, acPreview, , WhereClause

Exit_btnPreview_Click:
   Exit Sub

Err_btnPreview_Click:
   MsgBox Err.Description
   Resume Exit_btnPreview_Click

End Sub ' btnPreview_Click