Hi Ram,
apparently you are not sending enough information to radius for accounting. Starting 1.2.0 you need to add extra attributes since basic info doesn't anymore contain the necessary fields to build a cdr.
You should have something similar: modparam("acc", "radius_extra", " Called-Station-Id=$tu; Calling-Station-Id=$fu; Canonical-URI=$tu; User-Name=$au; Sip-User-Realm=$ar; Source-IP=$si; Source-Port=$sp; From-Header=$hdr(from); User-Agent=$hdr(user-agent); Contact=$hdr(contact); Event=$hdr(event)")
Cheers, DanB