Start off with a simple SELECT until you get it working.
Small steps, one at a time.
I cannot see why that would not work, I have used that syntax many times with out issues?
Code:
strRptQuery = "qryEmployeeHours"
Set ctl = Me!lstDayType
'Open the report with an OpenArgs value to get selected hours for employee
' Now select what type of day records from listbox
If ctl.ItemsSelected.Count > 0 Then
For Each varItem In ctl.ItemsSelected
strParam = strParam & ctl.ItemData(varItem) & ","
Next varItem
Else
MsgBox ("At least one Day Type is required")
Exit Sub
End If
' Need to pass the criteria as a string
strParam = " IN (" & Left(strParam, Len(strParam) - 1) & ")"
strParam = "[DateType]" & strParam
DoCmd.OpenReport "rptHours", acViewReport, , strParam, , "Selected"