As Sony updated the PSPs firmware, compatibility with certain PS1 games got broken along the way. For many of them, you'll want to be running a plugin called popsloader; it allows you to use the PS1 profiles from earlier firmware versions. I'm looking at this compatibility list, and both Rockman X3 and the european Megaman X3 are listed as working under the v3.52 profile.
You can find a proper tutorial for popsloader here: http://wololo.net/talk/viewtopic.php?f=17&t=7410
On the off-chance that doesn't help, have you looked into manually converting a Megaman X3 ISO into eboot format? Something like auto-popstation should work, and help you build a proper copy.
"I think that the problem with this video is it is highly derivative of many popular bands within the genre. Although when viewed on its own merits, it does have a deeper groove. However what it has in groove, it lacks in originality. One can't help but be reminded of such bands as Pearl Jam, White Zombie, Suicidal Tendencies and other bands that bear the mantle of so called "Alternative Rock". One is even reminded of Lorie Anderson when she wore curlers. Hehehmhm! This video speaks less to the heart and more to the sphincter. In closing, I think Korn would do well to learn more from -"