I agree with PatriciaObreja. However, if you are using the parameters as date in your record selection, then you will have more work to do
You need to create a formula to translate the string months into a month number
//MonthNo
Select {?Monthparm}
Case "January":
1
Case "February":
2
Case "March":
3
.
.
.
Case "December":
12
If you are selecting records based on month and year then
{table.datefield} in [dateserial({?YearParm},@MonthNo,1) to dateserial({?YearParm},@MonthNo + 1,1-1)]
-lw