I think that this is what you want to do:
 Code:
Dim $asCalMonths,$sLastMonthFile,$sThisMonthFile
 
$asCalMonths='December','January','February','March','April','May','June','July','August','September','October','November','December'
 
$sLastMonthFile=$asCalMonths[@MONTHNO-1]+(@YEAR-(@MONTHNO=1))+@USERID+".xls"
$sThisMonthFile=$asCalMonths[@MONTHNO]+@YEAR+@USERID+".xls"
 
"Last month file="+$sLastMonthFile+@CRLF
"This month file="+$sThisMonthFile+@CRLF