Hello guys if some one please can help me here..

Yesterday ive upgraded my php version from 5.4 to 5.6 .... everything was OK until today one customer complaining about seeing their mails ... the problem is that 1 specific email domain cant be accessed trough roundcube i am using virtual mails ..

On that domain if i create a new mail user everything goes as normal and it can be accessed using roundcube, send and receive mails if i delete an existing account and i create the same deleted account again the error persists in my error logs i got nothing till now but chrome browser says: HTTP ERROR 500

PD i am using ISPCONFIG+postfix+dovecot+roundcube

Thank You All.