You also didn't provide any details for anyone to be able to help you. Are you getting an error message, is so what is the error message? What happens when you try to register? What modules are you running? What template are you using?
Unless you can provide information all anyone can do is make guesses.
First of all, you can try to disable the Captcha module and antispam modules. After clear the template cache and try again. If still not working also disable Facebook module. Don't forget clear template cache every time than you disable a module.
Just for fun, and while I forgot where I grabbed the initial code..
“I suggest you use Winmerge to compare the source code between your old copy and the new version to...”
“Sorry to take a while to get back to you. I assume that you are still having this problem? I am...”
“Well there certainly isn't a simple way to do it, so I'm going to say no....”
“No, there are no plans. That doesn't meant that it will never happen, it's just not a priority....”
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