The compatibility checker would not check to see that it could access your MyBB installation. That is what is happening now in the conversion and it is stating that it cannot do so via the given path provided or the path provided is incorrect. If you are unsure how to ensure that permissions, ownership, and paths are correct, you may wish to contact a server administrator for assistance or simply, a second look (as we've all had those moments 🙂 ).
This may be obvious but some aren't quite aware so I will say it just in case. Keep in mind that your Invision Community instance and MyBB instance need to be on the same server to do this conversion.