For anyone reading this today 12/17/2018, if this is still occuring on your system. The issue is the settings for the session under the Security tab in globals. If the session time is set longer than the amount of time a session cookie is active on the local computer. This error will occur.
Example:
Local PC cookie set to expire in 2 hrs
Session expiration set in OpenEMR to 3 hrs
This will cause this error to still occur. If the default 7200 is left in the system This error will not occur.
A user had the security session timeout set to 36000. We changed it to 3600 and the system work normally. Error gone.
Cheers
@juggernautsei