The "activation" key is not what is used to log into the forums.

When you got your activation email, you put that "activation key" into a "signup" page where you also created a username and a password. 

All you need to do to login to the forums, is enter the username and password you created.

You can reset it here:

http://www.markettheme.com/wp-…..stpassword

The activation key proves your purchase of the Market Theme software (and is provided upon purchase).   The "support" forum is only available to paid members.