Since the issue is website specific, that suggests that the problem lies with that specific forum. Your user permissions might not have been set correctly by the forum owner or possibly your anti virus software is blocking requests from the site.
Might be worth seeing if creating another user account with a different user identity works properly. If it does, then the problem is with your original account settings on the forum. If not, then the problem is probably related to your computer settings, or possibly with your internet address block being blocked for some other reason.