Because it complains that Server Error
This server has encountered an internal error which prevents it from fulfilling your request. The most likely cause is a misconfiguration. Please ask the administrator to look for messages in the server's error log.
One of many problems with the management of this forum. You aren't the only one to see that sort of thing.
At the top of the thread you will see a "Feedback about Forums" link. That's the one that it was referring to when it said "Please ask the administrator to look for messages in the server's error log". Send them your complaint too. But don't expect a quick resolution, this place has been a mess for weeks now.