MIR6 - posting date check

Hello friends,

My requirement is like this .

while user is posting the invoice in MIR6, if the posting date belongs to Previous

Month, ( Eg: user is posting an invoice with Posting date 30.03.2007 in the Month

of April 2007 ), System has to throw an error in the screen asking the user to enter

the current date of current month.

shall i go for some user exit ?

Is there any user exit available ?

Please help me out .

Regards,

Hari Prasath.S