An error like this will appear whenever something unexpected have occured in system.
If the error seem to appear randomly then it might just be due to temporary issues in general in system.
If the error keep appearing after a certain action made in system then the error is might be due to system not being able to handle the operation. Try to figure out what seem to cause the error to occur, it could for example be due to fields not filled in correctly prior to the action made.
When you are logged into the system you also have to make sure to not having your user session in multiple browser tabs at the same time.