M fault error,m execution failed

Not familiar with the machine, but did a little research via google and it seems that their range of machines have auto tool changers. If this is true for your machine, does the issue occur on every tool change, assuming that the job needs more than two tools? If some tool changes work correctly but this one doesn't, I would suspect some sort of issue with that particular toolholder or the retainer attached to it. The spindle/toolchanger set normally senses whether the tool is properly installed with some sort of sensor on the tool release/ejector shaft. If that does not return to its normal 'tool loaded' position after grabbing the tool, it should generate a pause in the system, rather than allow the motor to start and spin an ill retained toolholder. If the tool holder is an 'odd' one with a slight deviation from standard, or the retainer screwed in at the top of the taper is longer of shorter than standard for the machine, this could trigger an issue like this. Then manual interference may reset the error flag allowing the system to run through second time around with the tool pre installed.
The only other thing that I can see that might cause the issue is some incompatibility between the data in the tool library, for example the tool position is question is used as a location for temporary tools and the tool has not had the zero depth set properly or left blank and the machine is indicating that it does not have information required to drive the tool as commanded, though I don't see why it would then work on the second pass.
My background was running an industrial 8x6 14 tool router for a number of years, there were still a lot of things that I didn't fully understand about that machine when we parted company. Typically cycled through 4-8 tools per program.