Locked user session

Hi Guys, PCLOS Trinity 14.0X For the past few days I have been getting a "Session locked by user" message with only user can unlock this session. I can enter my password and get in with everything working OK. If I reboot, hard reset, I don't get this message again when I login. I may not see this again for two or three days, and then its back. I don't normally leave the computer switched on so I might restart the computer twice a day. Anybody any clue as to why this has started to occur. Thanks in advance for any help. -- Best Regards: Baron