Cosmec conquest 525 error

Hi I was hoping someone can help with this error we are getting on our cnc,the error is “M execution failed”the program runs does 90% of the job then comes to its final tool change and stops once it picks up the tool,I then have to reset and run the program again and on the second run of the same program it works,I thought it was a bad program error but surely if it runs the second time it must be something more sinister that is causing the error,any help would be greatly appreciated.