I installed Vanillaforums, but I got this error when I try to visit my website:
Something has gone wrong.
We've run into a problem and are unable to handle this request right now.
Please check back in a little while.
It also is worth the effort to read the troubleshooting (and install) instructions here:
the instructions could be improved by adding an image to the screen similar to
reading documentation could also be useful. It is there for a purpose.
I may not provide the completed solution you might desire, but I do try to provide honest suggestions to help you solve your issue.