In a response to this thread,
I too have been having similar troubles signing in to the forums, since the recent forum upgrades. It turned out it was down to cookies themselves.
Firefox always works, I haven't tried in Internet Explorer because i hate it. However though, if you have trouble signing in with either IE/FFX/Opera you may use this thread to give you clues on what to do.
Otherwise, what you read below, is aimed at Google Chrome.
1. Open a new tab, then click the "menu" icon, afterwards click the "Settings" link, in the drop-down....
2. Once inside the "Settings" page, scroll down until you see a link "Advanced Settings"
3. Shortly afterwards, there's a section called "Privacy" , now click the button "Content Settings"
4. A new window pops up ---- > Then inside that window, click the button "All Cookies & Site Data"
5. Shortly afterwards a new window appears again, -----> Inside that window , type in "bmwforums" in the mini search box...
6. Now that you can see 2 cookies for this forum. Next thing to do is:
- Place your mouse over the site until it highlights in blue
- You should be able to see an [x] icon on the far right
- Click the [x] icon ----> This will delete the cookie
- Now, repeat this proccess for the SECOND link at the bottom (which starts with "www")
7. Afterwards , the cookies for BFI should be deleted from Chrome. Don't close the browser yet BUT close the Settings page as we're done with it.
8. Now, type in "bmwforums.info" and enter your user details again. Also tick "Remember Me" to make sure the cookie is saved for your next visit.
Now i don't have to use a crappy bloated IE browser, now that Chrome is fixed.
If any of you , have had success with this Guide , let me know please so that i know if this guide was useful or not.