one user cannot login, other can

Hi, I am using the M Social theme with an alternative login page for security reasons. Some users can login but there is one user right now which for some reason cannot login. No error appears. The user has been deleted and added again with different username and password. The email address remains the same and still cannot login. I need help to solve this issue.
website verenigingzonn.nl

please let me know where I can leave access details
regards
Geert

Hi,

Are you trying to login via Msocial popup form or the WordPress backend? Please check also the WordPress backend, and try to change your theme to default e.g. TwentyThirteen and check again, because I don't think that this issue is connected with our theme directly.

Hi
This issue remains when switching themes. It is related to using M social because of the way the settings are in the features for changing the login page -very complicated. If you cannot provide support please tell where to address this issue.

regards
Geert

If you have also this problem with default theme, like TwentyThirteen, you should ask on WordPress forum.
http://wordpress.org/support/

If you can, send me a PM with backend access to your website (send me also the login and pw of user who can't login), then I'll be able to check one more thing.