Hi Mohit,
In testing locally on 12.9.01 I simply selected 'Attachment Mandatory' for a service option and received the following when trying to submit a request for the same offering/service option:
To submit this request, you must add an attachment to the service option(s) <service option name>. Use the Attachment icon of the service option.
I did notice the following included in CP1, not sure if that's what you're running into:
T58S008
Though the ‘attachment mandatory’ is enabled at service option level, a request, created through ‘Copy Request’ feature, can be submitted without any attachment, if the request has ‘One-Click Submit’ Service.
Thanks,
Jason