N64: Playing NTSC games on a PAL Machine

[gotmished]

Hello There,
                       I recently purchased an Ultra SFX 64 Universal Game Adaptor V3 for my PAL system in the hope that I can play Ken Griffey Jr.'s Slugfest, among other things. Now, I know it works because it boots my PAL games with another PAL game in the back, but when I try to boot my NTSC copy of Slugfest the screen flickers for a second, as if it is going to run the game, but the the screen then remains blank. This also only occurs if I use my PAL copies of Smash Bros., Banjo Kazooie or Pokemon Snap in the back of the converter; all of my other PAL games can't even achieve the promising flickering of the screen.

I've even tried using a TV that has an NTSC system setting, but to no avail.

Any help would be greatly appreciated as to what I'm doing wrong here.
Sincerely,
Hamish

P.S: If it helps, I also own a Game Booster with built in Action Replay V3. I have already tried the inbuilt key code for Slugfest, not to mention several other key codes I've found on the internet but Slugfest never starts when I swap the carts over. The nearest I got was putting the SFX (with Slugfest in it) on top of the Game Booster, and the Action Replay screen actually loaded! However, Slugfest still wouldn't start when I opted to start the game without any codes activated.