When running a business process a user may receive Error: 'An error occurred before executing the process 'Business process': The business process 'Business process' is already running' even though the process was never kicked off again. The error may be followed by Error: An unknown error occurred during the request. This could indicate a request to an invalid endpoint or a problem with the web server configuration. Despite the errors, the process still completes successfully.
Download and install the latest patch which contains all fixes from previous patches. If you are running an older version, download and install the latest version and then the patch.