Hello everyone.
I have a wordpress 3.5.1  with Simple Press  5.2.6.

I'm migrating a wp forum, which has more than 15,000 forums posts in each forum, or even more.
The problem is that when I try to migrate forums with so much content, it returns "500 internal server error".

And in the server log, "Error MySQL server has gone away".
Someone can help me?
Maybe someone already passing through the same problem.

so its sounds like your server is running out of php memory or cpu time available to perform the import...  can you try increasing both in your php.ini file to allow the import to run?