It is frustrating creating some account at a given desired port, fill all the form, and when clicking create a pop up message states the port being in use.... and your form is gone!!!

Wouldn't it be better to check for port availability PRIOR to perform form submit?
I would like having a form validation like if incorrect password settings or so... where an indepent window informs of the error, and lets you correct while keeping all the input data.
It would be great if it could inform the user that the port is un use.

An admin user could be told the port is in use by some account or some external service (operating system related, etc...)
A reseller could be reported a port being in use by some of their accounts, or a plain already in use if the offending port does not belong to some of their accounts.