PixelmonDoesntWork

please. i have googled everything. i have tried everything. there is no help and nothing else i can do. idk if anyone even goes on this anymore since it has been like 4 years but i need some kind of help if they do. i am using pixelmon 6.2.3. everytim i go on single play it kicks me off saying fatal error, then it puts me on the multiplayer screen. I go on an official pixelmon server on multiplayer with the same version of pixelmon as me and it loads for a second then kicks me off saying fatal error. i have uninstalled and re installed forge and pixelmon like 3 times.i have googled like 30 different things to try and get help. theres nothing. if anyone sees this. please help