2 errors for new user regs

Hello everyone..I was wondering if you could help..I have 2 different new forums..on one when someone tries to register, they get this
Adult Insiders - Error

This action is available via POST only. Please press the back button and try again.

this is after filling out all the required reg info..

On my other site no one gets an email for confirmation.I am pretty sure i have everything set up correctly..any help is appreciated
I deleted the custom style and just have the original default and it still seems to be doing it..I have tried reg myself 2 different times under another email