Over the last decade or so I have tried twice, with two different, experienced and highly qualified hypnotherapists that specialise in past-life regression. Neither one of them could even get me into a light trance, with multiple methods, let alone regress me to a past life. The latter of the two had never experienced a failure like that with her techniques.
The only clue as to why this occurred was offered by a medium friend some while later. He claimed that the vibrations of these two hypnotherapists were (I hesitate to say 'not high enough') insufficient, for the task.