How would I get the previous month?

I need my file to be renamed Mods201001.xls.

Here's what I have

@[User::SharePath] +

RIGHT("0" + (DT_STR,4,1252) DatePart("yyyy",getdate()),4)+

RIGHT("0" + (DT_STR,4,1252) DatePart("m", getdate())-1,2)

But I get an error -

Attempt to set the result type of binary operation ""0" + (DT_STR4,1252)DatePart("m",GETDATE))-1" failed with error code 0xC0047081