Just downloaded it from https://github.com/coppermine-gallery/cpg1.6.x-plugins (https://github.com/coppermine-gallery/cpg1.6.x-plugins)
I'm using the curve theme for testing the plugin (clean, unedited).
Works fine but if I copy and paste from the sample theme to the curve theme the function <<<theme_display_thumbnails>>> I get the blank page with the error:
Fatal error: Cannot redeclare theme_display_thumbnails() (previously declared in C:\Apache247\htdocs\cpg16\plugins\usergal_alphatabs\codebase.php:41) in C:\Apache247\htdocs\cpg16\themes\curve\theme.php on line 903
If a user needs the function in his theme, the plugin becomes useless.