Error in META_ATTACHMENT_CREATE

Hi Experts,

     We are using SRM 701 , ECC 6. We are using extended classic scenario.  we are trying to transfer PO attachment to back end , but when I am trying to execute the FM "META_ATTACHMENT_CREATE" it is showing an error. when i further debug in to the FM module i known that the error is

" The link to SAP object is not allowed for document type SRM".

       I added an entry in DC10 as SRM for Config purpose. Please let me know why this error occurs and what is the solution for it?

Thanks & Regards,

Aishwarya.M