yes the blocked cookie could do it - i should probably add a message about having to have cookies enabled.
But the fact that it's recognizing you on the forum should mean that it can see the cookie.
The cookie name should be SMFCookie879 from the donationcoder.com website.
My experience has always been that for every person nice enough like you to report and help figure out a problem without losing their mind, their are 20 others who just get very angry and leave, so i really do appreciate your good nature about this and i assure i will help you get it resolved if you stick with it
See if you can find the cookie and allow it.
ps. regarding blocking cookies:
As someone who used to be paranoid about cookies, what i do now is allow all cookies, and then use a program that will delete all cookies except the ones i specify when i run it occasionally. I think this makes 1000x more sense than blocking cookies from ever getting on your pc, since so many sites need them for temporary things. The real concern about cookies is not them being on your pc, but of them identifying you over time, so by letting them get put on your pc but periodically deleting them, you get the benefits without the drawbacks. just my 2 cents worth of opinion. might be time for a thread on good cookie cleaning software..