After upgrading to 12.1 RU5 and reconfiguring symbolic links on the Inetpub/content/ folder, clients and GUPs receive HTTP 403 Access Forbidden results in the Apache Access logs.
From the Apache Access.log you see repeated GET request results such as this on all GET requests hitting the apache server:
"GET /content/TempCache/{810D5A61-809F-49c2-BD75-177F0647D2BA}/150426016/xdelta150426016_To_150507009.dax HTTP/1.1" 403 301 "-" "Smc"
Additionally, the Apache Error log contains the following symbolic link errors that look to be concurrent with the access log's GET requests:
AH00037: Symbolic link not allowed or link target not accessible: C:/Program Files (x86)/Symantec/Symantec Endpoint Protection Manager/Inetpub/content