Cannot submit form on CiviCRM 4.7.7, might be related to CRM-18510?
This looks likely to be the same underlying problem as the issue described in CRM-18510. There's a fix referenced there: https://github.com/civicrm/civicrm-core/pull/8317 . If you test this out, do report your findings here and on CRM-18510 . Hope it works for you.

Regards,

Dave