Endpoint Protection

Hi All,
We are having a problem post OS install (automated) with our SEP 12.1.3001.165 clients. I am seeing the following errors in the Symantec event logs and the Client System Logs. 
Content download to the client failed
Product: SEPC Virus Definitions Win64 (x64) 12.1 RU2 H
Version: MicroDefsB.CurDefs
Language: SymAllLanguages
Moniker: {07B590B3-9282-482f-BBAA-6D515D385869}
Sequence: 150407057
Publish Date: Tuesday, 7 April 2015
Revision: 057
Source: Group Update Provider
Size: 658730860 bytes

The client will continue to fail from the GUPS for 10 hours until it fails over to the SEPM for the 'SEPC Virus Definitions Win64'. From then on it downloads the 'SEPC Virus Definitions Win64' content from the GUP's ok.

Interestingly while the 'SEPC Virus Definitions Win64' fails to download content from the GUP's other content is downloading from the GUPs ok on the same workstation e.g;
SEPC Extended File Attributes and Signatures 12.1 RU2
SEPC Behaviour And Security Heuristics 12.1 RU2
SEPC Submission Control Data
SEPC Iron Revocation List 12.1 RU2
SEPC CIDS Signatures 12.1 RU2
SEPC Iron Whitelist 12.1 RU2

I am seeing behaviour on multiple workstation. I am going to have a challenge making a change to the client to enable the sylink.log logging. Is there any methods I can use to diagnosis this post-mortem?

GUP cache size is 500 MB deafult, its requesting 600 MB, (658730860) try increasing the GUP cache size and , yes please post a Sylink.log from affected clients,

Can you enable sylink debugging on an affected client and post the log here?

You may need to increase the GUP cache suze to something like 2048.