Save button does not work with "restored" data xml file. gnucash-2.4.11-1.el6.x86_64

[Jean-David Beyer]

My old computer died (four loud bangs and smoke came out of the power 
supply) when the power came up after Sandy, so I got a new one. The new 
one has a 4-core Xeon 64-bit processor. The old one had two 
hyperthreaded Xeon 32-bit processors. That probably has nothing to do 
with it.

The old machine ran an older version of gnucash, the new one uses 
gnucash-2.4.11-1.el6.x86_64. My OS is Red Hat Enterprise Linux Server 
release 6.3 (Santiago). The old one an RHEL 5.

I copied all my files, from a directory named Gnucash from the old 
system backups to the new machine into the same directory. If I open 
that with Gnucash, it comes up just fine. But when I go to hit the Save 
button, the button is grayed out. If I select File, Save is also grayed 
out, but I can write if I use the Save AS button to a new file.

Obviously, I have overlooked something. What?
How should I go about debugging this? I assume I failed to restore a 
needed file, failed to set some permission correctly, or something like 
that.