Obviously the paths had changed so I did a Search / Replace across all the Netbeans project files.
Then got an error:
... \nbproject\wsit-deploy.xml:12: Must set Sun app server root.
Clicking on that line showed:
unless="sjsas.root" Must set Sun app server root
For once, Mr. Google failed to come to the rescue.
Eventually, I brute force searched the actual Glassfish installation under:
system-property name="sjsas.root" value="...\Program Files\glassfish-3.0.1"
Damn - wrong path.
Moral of the story. When you migrate projects across machines, you may need to update the Glassfish configuration files as well as the Netbeans project files.
Note: The ... above represents the actual directory which is different in each environment.
Aside: Because this was a Glassfish issue rather than a project issue, I got the same error when I tried using Tomcat instead of Glassfish. Maybe that should have been a hint!