Its a bug it effects ASRs, , 3700s, 2900s etc there's a different bug id for each platform
I would TAC it to find exactly what your id is and if there's a fixed release for your platform as i checked your caveat release and its not in there or you could just try upgrade to latest safe harbour image SY5 looks like it was release 7 days after your version
%ENTROPY-0-ENTROPY_ERROR: Unable to collect sufficient entropy on bootup
CSCum86316
http://ccieplease.blogspot.ie/
http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst6500/ios/15-2SY/release_notes/release_notes.html#pgfId-5233343