Sorry about the issues you are experiencing "Bicycle Rider" and "o2kayak". There are two possible ways to save your authentication credentials for the forums. The forum software will set a browser cookie that will keep you logged in for the amount of time that you specify. The screenshot below shows these options. If you do not allow cookies or use some type of browser add on or software to manage or delete cookies it could cause the issues that you are describing.
The other possibility is that you are allowing your browser to save the username and password and populate it into the login form when you arrive at the forums. Browsers save this information based on the domain name of the site and it is possible that you could run into problems if you also have an account on our main site that is different than the account credentials that you have for the forum. In this situation your browser may load the credentials that it saved for your MyACA account from the main site instead of the account info for the forums. This is something that we would like to address in the future, but do not have a specific timeline at the moment.
I typically use the first method to save my forum credentials and have not had any issues since we have been running the current forum software. Hope this helps to clear up the issues you are experiencing!