Export licence validity date

Hi,

My customer requirement is to throw an error when an user is trying to provide an export licence in the sales order which was expired some time back. I would like to know whether we do any sort of customization for this or could u pls. help me out in handling this issue. The crux of the requirement is that the SO should n't be save when an expired licence number is provided in the sales order. Your reply will help us in cracking the issue.

Regards,

Madhu.