NAV Server (NST) crashes with message "The process cannot access the file '.

Hi, sometimes the Windows Client can not longer connect to our NAV Server, the Service is still running but Connection is not possible, the Event log Shows the following error:

The process cannot access the file 'C:\ProgramData\Microsoft\Microsoft Dynamics NAV\70\Server\MicrosoftDynamicsNavServer$navrtc1\source\Query\Query50000.cs' because it is being used by another process

Does anyone have an idea what the reason for this error message is?

Regards

Mathes