In that case, that's quite likely the cause. Either the file is corrupted, or the changes have resulted in an inconsistency/conflict in the data that's causing a crash.
Without knowing what you changed with RED MC, I can't suggest anything specific beyond undoing those changes, i.e. changing the values back to what they were before. If that doesn't fix the problem, then your only option is to restore from a backup if you have one, or start over.
My guess is that trading your player has resulted in some conflicting/incorrect values that are causing a crash. Again my advice would be to undo the changes you've made and restore the values to exactly what they were before, and see if that resolves the crash. If not, you might need to start over, unless you have a recent backup of the save file before you made those changes.