Tim,
To determine if its something in your model causing the issue, you can try the following:
If the new project successfully deploys, the problem is in the sandbox node of the original project. You can file a support ticket with Mendix to resolve that.
If the new project does not successfully deploy, there is likely something in your model causing the issue. You can look at the build log on your original cloud node to see if there are any obvious issues reported there. You may find that a widget or module you added around the time that it stopped working is causing issues.
Hope that helps,
Mike