Default Theme Directory Error

[Azu]

I'm getting the following error:

"The default theme's directory is wrong, please correct it by clicking this text."

When I click on the text, I get this:

"Not Found
The requested URL /Forum/index.php was not found on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request."

I tried using repairboards.php, but I just got a page that said "hacking attempt..."

I'm new to all of this, so I'm going to need an explanation that's dumbed down 

What do I need to do?

[Azu]

I think I'll just delete the forum applications and start fresh.

These errors could have occured when I switched servers.

[xenovanis]

What is repair_settings.php?