How to program new keys/fobs for used Jeep Grand cherokee we just purchased?

We purchased a 2004 Jeep Grand Cherokee used last month and it only had
one key and a fob that didn't work at all. We purchased 2 new keys and fobs
and hired a locksmith to cut keys and program fobs but he can't get them to
work. He has told us that maybe the ECM was changed? The keys start the
jeep but it shuts down after a few seconds and everytime he tried to
program, he gets errors saying invalid.