The message exit value 18446744072635809797 is seen with many solvers. It indicates that the solver has crashed, but does not provide any specific information as to the cause. In my experience, the most common cause is running out of memory, but other causes are possible.
To give more definite help, we’ll need to get some more context for the error. As a start, copy all of the AMPL output in the run where you get the “exit value” message, and paste it into a reply in this Discourse thread. Then it should be possible to give you some additional instructions for troubleshooting the error.