Unable to log in to CP after upgrading to EE 2.7.2

I have just upgraded EE to version 2.7.2 the front end of the site is working correctly but I am unable to log into the CP. The log in screen loads, on entry of my user credentials it reloads and blanks both fields.

Tried entering a incorrect password and received the correct error message. Used the forgot password form successfully and reset my password successfully but still have the same issue.

On referring to other entries on the forum, I dumped all the entries in the DB table ‘exp_password_lockout’ this didn’t fix my issue either.

I’m at a somewhat crucial stage of development at the moment and really need some help here.