You tried both 50 and 60 htz, and neither of them worked? Weird.

Well, on the site - ####://www.dccopyworld.com/ - Under DC Files-->DC Utilities, look under "Patch Tools". You'll see a Dreamcast PAL-2-NTSC Patcher. I think the file you'll need is the PAL Patcher.

(I've never had this problem before, and never had to patch any games - so I'm not 100% sure that this will solve your problem... Since nobody else replied, I guess this is the best advice you have for the problem.)