Why did you 'upgrade' to 7.3? 7.4 has been out nearly 6 months and 7.5.1 is the current version
Most likely your errors are fixed in the current release, I'm not sure if 7.3 has it, but in more recent versions - the control panel has a 'permissions' link at the very bottom of the left column that may be able to tell you what's going on.
It's also possible the verification email is getting trapped in their spam folder - have them add your site to their safe list.
