There are many reasons why this happen. Two of them is that the forum can not connect to its database which tends to crash and won't let you view the current page, and the other is that some malicious script is being injected into the forum so it crashes the website (these are only my opinion). If you see this message, just wait for few minutes and refresh the page. If the message still there, then you have to wait for longer time. We can not do anything about it since only the Admin has the right to configure the website and database.