JMeter - Could not find the TestPlan class

I had the same problem today with JMeter 2.13. When I saved it using this entry from the menu I received a jmx file that was accepted in non-GUI mode:

I too had the same error message. After creating the Test Plan and successful trial run on a Windows machine in GUI mode, I uploaded the JMX file to a Linux server to run in Command line mode.

After much searching and messing around I found that it was because I left the Test Plan name of the script to the default "Test Plan"!? When I changed it to "My Test Plan", for example, then saved and uploaded to the Linux server it ran successfully.