There is in fact a bug in the new WP-Members 2.7.1 release. However, there is also something else that is not a bug but could generally be confused as one. Hopefully, this post will clear up any confusion, help you get things fixed, and keep your site running smoothly!
First, the non-bug:
The new version added some enhancements to prevent non-activated users from logging in via the back-end login. Prior to 2.7.0, this wasn’t needed because the user did not have their password. With the addition of the option of user chosen passwords at registration, we needed to add a check for the active flag as part of the user’s credentials.
Enter the non-bug. All users are checked at login to see if they are activated. Yes – admins, too. So admins that are being “locked out” are most likely being prevented from logging in because their profile is not activated as far as the plugin is concerned.
The fix? Make sure all admins are activated profiles. If you have several, you can just go to the Users > WP-Members menu item and activate them all at once.
(For those of you who may be wondering if you have inadvertently locked yourself out, this only effects users of the plugin who have multiple admins. There has always been a feature that sets the admin who is setting the plugin option of moderated registration as active so that they are not inadvertently locked out. So, the primary admin should never be locked out.)
Now the bug:
There is a bug that I have found that causes a user to be deactivated if their profile is updated by an admin using the profile.php page (the WP admin backend). This has been corrected and is now available as the 2.7.2 release.