Problems uploading and maintence script fails to complete (keeps resetting)

We have been running gallery 3 for some time now and are starting to get errors when uploading files.

The error message is "Unable to process this file".

I checked var/logs and I see a lot of these error messages when uploading:

2014-04-07 15:37:26 -05:00 --- error: @todo UNABLE_TO_LOCK_EXCEPTION
#0 /var/www/html/gallery3/modules/gallery/libraries/ORM_MPTT.php(50): ORM_MPTT_Core->lock()
#1 /var/www/html/gallery3/modules/gallery/models/item.php(369): ORM_MPTT_Core->save()
#2 /var/www/html/gallery3/modules/gallery/controllers/uploader.php(74): Item_Model_Core->save()
#3 [internal function]: Uploader_Controller->add_photo('30093')
#4 /var/www/html/gallery3/system/core/Kohana.php(331): ReflectionMethod->invokeArgs(Object(Uploader_Controller), Array)
#5 [internal function]: Kohana_Core::instance(NULL)
#6 /var/www/html/gallery3/system/core/Event.php(208): call_user_func_array(Array, Array)
#7 /var/www/html/gallery3/application/Bootstrap.php(67): Event_Core::run('system.execute')
#8 /var/www/html/gallery3/index.php(102): require('/var/www/html/g...')
#9 {main}

I read some related topics, mainly http://galleryproject.org/node/97321 and http://galleryproject.org/node/99096
This suggested following the instructions at http://codex.galleryproject.org/Gallery3:FAQ#Why_do_I_get_a_Error_.232038_when_I_try_to_upload_more_than_one_item

Which I followed by updating max_file_uploads. This still didn't fix the problem, so I ran the "Fix your gallery" maintenance task, which failed to finish, replicating this issue exactly: http://galleryproject.org/node/106215

Data was corrupted, but lucky I was able to restore from a backup.

I'm curious if I simply have too many photos? There are 22k+ photos across 4 albums (most of them in one album). What is the max amount of photos that can live in each album without casuing problems? Would it make things run smoother if I moved photos out into smaller albums?