Multi-User Harvest (Remote) Agent is being used. Initially do a Sync Checkout against this agent. If it succeeds, repeat the same Sync Checkout. Intermittently you may get the above Checkout error.
If a Browse Checkout was used, there's no error.
The error E03060086 would usually occur because of the umask value used when the Agent was started. In a multi-user Agent - shared working environment setup, a umask of 002 is needed before starting the multi-user Agent.
Default umask on most UNIX systems is 022 . Refer to your UNIX manual/system admins before changing this to 002 and starting the agent.
Below commands should let you reset the umask and start the agent (you'd have to shutdown the agent first)
umask 002 agntd
If the Unix user using the agent (for checkouts) is same as the owner of the signature files on that agent machine, then umask of 002 is not required. Contact CA Support in such a case.
If the problem persists even after using umask 002, contact CA Technical Support.