Sorry for not getting back to this sooner. I just tried to register and see the same error page. Can you try and check the following things:
1) Disable any JLinked Profile plugins that you aren't using or don't have the 3rd party extension installed for. So, if you have the Community Builder plugin enabled, make sure you have CB installed and actually want to import information into it. Do the same for K2, Kunena, etc.
2) If you're using a 3rd party SEF extension, please tell it to 'skip' JLinked so that it doesn't try to alter our URLs. LinkedIn and JLinked are very specific about the URLs they need to communicate, and if they are altered, that can cause issues.
3) If that doesn't work, in the Global configuration area of Joomla, set Error Reporting to "Maximum" and turn gzip compression off. Then, try to recreate the error. Hopefully there will be a prettier error message there that will help explain the problem. If so, let us know what the error is.
Let us know how that goes, but if it doesn't fix or narrow down the issue, just let us know!
Thanks,
Alex