This is probably due to a problem with the initialisation of the corresponding Linux app, which has prevented it from starting properly. You can start the Linux app from the command line in the "Terminal" app to see the messages printed on the standard output, which will help you to locate and solve the problem more quickly.
By the way, yes, you need to know how to start Linux app from the command line interface as a prerequisite, this is apparently outside the scope of this question :p