Why will Month() work, but MonthName() won't work in my textbox?

[Seth Schrock]

I've got a textbox on a report that I'm using to pull the month and year from two textboxes on a form. The following code works in the data source of the textbox:

="Billing Period: " 
& Month([Forms]![frmCustomer]![txtStartDate]) 
& " " 
& Year([Forms]![frmCustomer]![txtStartDate]) 
& " - " 
& Month([Forms]![frmCustomer]![txtEndDate]) 
& " " 
& Year([Forms]![frmCustomer]![txtEndDate])

However, I would like to make it so that I get the name of the month instead of the number. So I tried the following:

="Billing Period: " 
& MonthName([Forms]![frmCustomer]![txtStartDate]) 
& " " 
& Year([Forms]![frmCustomer]![txtStartDate]) 
& " - " 
& MonthName([Forms]![frmCustomer]![txtEndDate]) 
& " " 
& Year([Forms]![frmCustomer]![txtEndDate])

When I preview the report, however, it returns #Func!. Is the MonthName() function not available in this situation? I don't get any syntax errors while in design view of the report. I even tried adding the ,False to the MonthName() function in case it wanted me to explicitly declare the default, but that didn't change anything.

[ADezii]

The MonthName() Function does not accept a Date as an Argument, but a Numeric Value between 1 and 12, as in:

Debug.Print MonthName(1)  'returns January
Debug.Print MonthName(10) 'returns October
Debug.Print MonthName(4)  'returns April
Debug.Print MonthName(8)  'returns August
Debug.Print MonthName(6)  'returns June

What will work is:

'Returns November
Debug.Print MonthName(Month(#11/5/2011#))

[Seth Schrock]

Okay, that makes sense. Thanks.