Initialization failed after Sitefinity upgrade from 6 to 9 a

Had some fun upgrading a Sitefinity project from 6 to 9. After some clean up of the dll's, I got the project working in my development environment (laptop + visual studio). Then I publish, and move over the database and project. I get the cog wheels turning, then 'Initialization failed'. 1 error(s). Object reference not set to an instance of an object..... 

There are no error messages and nothing in the error or trace log... I'm pretty sure it's not the environment, because I can setup the 6 version of the project and it runs good. But I put in the 9 version and I get an ambiguous error message and no logs. 

Where can I find out more information of this error?

Hi Charles,

I already helped to some people with my solution in similar problem 

Please  try to follow this steps

0) Create backup for DB and files
1) Go to App_Data\Sitefinity\Configuration\SystemConfig.config
2) Comment all child nodes under <systemConfig>
3) And run your project again

Please let me know about your results

Hello,

Recently I upgraded a site from 8.1.5820 and we ran into the exact same issue during upgrade: No error/trace log, and instant failure with a nonsensical "object reference" error. Following Victor's steps made it work for us.

Victor: What is occurring in this scenario, and why did wiping out SystemConfig.config make the upgrade work correctly?

Fortunately, this solution helped for many people.

I don't know what is causing this issue. I can just guess. I think that Sitefinity can't find one of the modules by name, defined in SystemConfig.config and crashing with null exception.

Would it be possible to create an item in the feedback portal? Something along the lines of "Sitefinity should be more descriptive in its update failure messages when an assumption being made (such as a module name assuming to exist in SystemConfig.config") ends up not being true"? Especially in the cases where Sitefinity ends up logging absolutely nothing?