What can I do when I have forgotten my LastPass Master Password?

According to their site there are 4 steps to follow:

1) Attempt to login through the LastPass website at https://lastpass.com/. If you are able to login via the website but not via the plugin, this is likely a problem with the LastPass browser add-on, in which case you should report the problem to us directly.

2) If you cannot login through the website, try the password hint that you setup for yourself when you created your LastPass account. The password hint is not your Master Password.

3) If the password hint doesn't help you, go to the account recovery page to activate your local One Time Password and recover your account. Follow the instructions there - if the first computer on which you attempt access doesn't work, try the same process on any other computer on which you have previously accessed your LastPass account.

4) If at this point you have failed to remember your password, your account hint didn't jog your memory, and you've tried the password recovery on every machine you've logged into, your only recourse is to delete your account and start over.

It looks like you've done the first two. The third option somehow allows you to get a temp, local password. If that doesn't work, the situation doesn't look good.

Can't you just revert your password to the last one like it's stated in the most recent blog entry on the site you provided? - Or am I missing something.

Many users are changing their password and then determining they can't remember it, a number have also run into issues with password changes and want to go back, you can now do this yourself without contacting us: https://lastpass.com/revert

It allows you to either roll back your last password change or revert your account to the 4th. You must prove access to your email again to use it.