Hi Eswaran,
This is a fairly common error and it might have multiple reasons. I presume here your documents are ArchiveLink based and reside in an external content repository, either SAP Content Server or any 3rd party repository such as OpenText.
First I would try transaction OAC0 and locate the corresponding content repository. Validate the settings, especially the HTTP server name and make sure the server is there and is accessible from SAP. You may get this error if you have security enabled on this content repository (look for a check box "No signature") in OAC0 under full administration and there is a security certificate mismatch, in which case you might need to re-send the certificate from OAC0 or even generate one in STRUST.
Good Luck,
//Peter