If you can't login, it's most likely because you have your username or password wrong.
To recover your details, go to the members site login page: https://dmpmembers.com/members-login/
Underneath the login form you will see a 'Lost your password' link.
Click on that and reset your password.
Then, go back to the members site login page and login again: https://dmpmembers.com/members-login/
Be sure not to forget this second login step. You need to login back at the members site, or you may be lost in your profile.
These password instructions here may also be helpful.