I just upgraded to 1.4.20 and it works!
Now I have what appears to be a duplicate set of tables in the database, one prefixed cpg14x and one prefixed cpg132.
Are they redundant and can I safely drop the cpg132 tables?
That means you didn't upgrade correctly. Check include/config.inc.php and see what prefix Coppermine is actually using.
// MySQL TABLE NAMES PREFIX
$CONFIG['TABLE_PREFIX'] = 'cpg132_';
Can I edit the file to correct it?
Or is it more complicated?
Don't change the file. That means you can drop the cpg14x tables. Check them first though to make sure they don't have anything you want.
thanks