Error when attempting to edit resource

Just had an email from a client who's getting the following error:

Fatal error: Call to a member function addLexiconTopic() on a non-object in /home/site-user/public_html/core/cache/includes/elements/modplugin/6.include.cache.php on line 56

It only ever happens when you click on a resource from the side panel. I've tried manually clearing out the cache, but it returns each time. Front-end is working just fine, but obviously she can't make any changes atm.

Any help would be gratefully received.

See what Plugin has id 6. You will need to diagnose the problem with that Plugin, or disable it for now, to solve this problem.

Thanks.

Turns out to be the Gallery plugin - it's been buggy for a while now
Would you, or anyone, happen to know if I can do an uninstall/reinstall without losing gallery data?

I'm having this same problem! After setting up a big fancy gallery.

Is there any way to uninstall & reinstall the plugin without destroying my data?

I couldn't do anything from Package Manager.... It never finished 'updating' ... now Gallery shows as 'uninstalled' ... and won't 'install' ... even though it's working. I just can't edit Resources!

Using MODX Revolution 2.1.5-pl (advanced)

HELP! Thanks!