[SOLVED] Upgrade to CB 2.03 causes blank screen - front and back end

I am running CB 1.91 on a Joomla 3.3.6 site. When I install CB 2.03 at first the installation page seems to lose its CSS - it's basically all menu. On the front end things work but the log in module shows the translation constants, not the values. On the browser (Firefox)tab I can see Error: 1062 - the whole thing is in the screen shot. Going back to the back end, after shuffling around I get the message the install wasn't complete and click here to finish it. When I do I get the welcome screen stating CB 1.91 is installed. Any further action causes the screen to go blank. Clicking the back arrow brings it back, other components seem to work fine but any attempt to use CB gets the blank screen. The front end goes blank totally.
This is the second time I've tried it with similar results.

Your migration failed for some reason. The key CB Articles is trying to use is reserved. Nothing else should have that key. Did you move your site or restore it with Akeeba backup or any form of backup software? This can sometimes cause the auto increment of your tables to break and that looks like what has happened as plugin ids don't start until 500 so nothing should be using ID 17. Please review the _comprofiler_plugins database table and see what is using the ID 17.

Thanks - my site isn't big but it's old. It has been migrated from 1.5 to 2.5 then to 3.0 and it's been restored with Akeeba many times.
The _comprofiler_plugin table (there's no 's') shows # 17 as
Name:CB Profile Gallery
Element: cb.profilegallery
Type: user
Folder: plug_cbprofilegallery

Maybe I should uninstall CB 1.9 first and try again?

An older release of Akeeba Backup had issues with auto increment not being restored properly so that could be your issue. The plugins table auto increment starting at 500 has been around for quite some time so going from J1.5 and wouldn't be the problem. The only way to really fix your issue is to re-increment your table, which is going to take quite a bit of manual work. The alternative is since profile gallery is taking the id you can try uninstalling profile gallery then installing CB 2.0. Uninstalling CB 1.x won't your issue and result in your CB configuration being lost.

To re-increment your table you'd need to move all the non-core plugin ids to be 500+, adjust the pluginid for the tabs, and their fields. Core plugins have the iscore column set to 1. Once done under operations in phpmyadmin you'd need to fix the auto increment value for the table.

OK I'm going with the first (easier) option. Is it the CB Gallery module I need to uninstall or is it something that has to be done through CB itself?

It's CB ProfileGallery within CB > Plugin Management that's taking the reserved ID. You may have more plugins taking reserved IDs though and the problem will just get worse with future releases as more core plugins are added.