Production Site and 404's

I have developed a custom CRM locally on my machine, and have a staging version in a subdirectory of my portfolio site for the client's office manager and me to test - no issues.

We're ready to launch, so I FTP'd the application to a subdirectory of the client's site, changed everything to point to their database. I get the login page, but when I log in, I get taken to a 404 (Error 404: NOT FOUND! This domain name has just been registered.) message that the Hosting Provider uses for parked domains.

Where should I be looking to troubleshoot this issue? Is it a problem with the hosting provider or did I miss something when I deployed the application? My portfolio site is on Godaddy (no problems) and the client's site is on 1and1 (problems).