When you test the robot.txt in webmaster its is checking that it gets a 200 response by accessing the robot.txt file, not errors within.
To check the errors within the robots.txt you should look at the crawl errors, that will tell you where the errors are like, page not found etc.
Your a forum owner, guess the owners here don't want to allow the uploads
I can't blame them, so much stuff builds and just gets left it adds up after years.
