Did I miss a step when copying a project to a new computer AND upgrading to RH 10?

I was given a newer, faster machine to use solely for Help, so I installed RH 10 HTML on the new machine only and then copied all the project files (originally built in RH9) to the new machine using identical file structure. I upgraded the project when prompted and everything looked fine--no broken links and all linked docs still in sync--until I tried to view the project. I can generate (WebHelp Layout) without errors and view individual topics locally, but Internet Explorer says it cannot display the page or find the file when I try to view the whole project. Troubleshooting the connection issue yields the message "The website you are trying to reach does not appear to be valid." I have just started a new project in RH10 on the new computer, and it displays fine, so I think it has something to do with either the copy or the upgrade process.

Things I have already checked: file paths to output file, default topic, and start page (in WebHelp properties and in Project Properties). IE does appear to be trying to open the correct .htm and is looking for it in the right folder.

I also searched for guidance on the proper way to copy a project to another computer, but to no avail, so it is possible I did it poorly. If there's a trick to that, it would not be all that difficult for me to delete the project on the new machine and start over with copying it the right way--everything is still intact and up to date on the old machine.

What else can I check or try? Thanks in advance!