The site that I'm having problems with is a paid site. I actually went into my account (control panel) to try and figure out the problem but wasn't able to access my own domain even from within my account. I'm experienced with using FTP software and have never had this problem before even with the free accounts that I had years ago.
I was told that it would take 24-48 hours for the fix to take effect and it's been a lot longer with more damage added to the problem. The technician reset the DNS records and made some changes to .htaccess which now has an effect on a very important email account that I have with Google, which means he changed the MX Records also!
In the meantime, I had to copy all of my web pages to another domain that I have, then redirect the URL to the other domain. Now the technician says, "I will need to remove the forwarding to see the site and the error in order to replicate and test the issue."
What's that got to do with a 550 error and a MX record problem? I'd really like to know how the 550 error occurred in the first place. With my understanding of domains I just can't see what removing the redirection of the URL has to to with a domain being locked. As I've already told the technician, if he would just fix the 550 error I can correct the MX Records myself.