Starting with Breadcrumb NavXT 5.0.1 (and running through the 5.1.x releases) the message below may appear when you update the plugin from a pre 5.0 version (e.g. 4.4):
Breadcrumb NavXT was just updated from a pre-5.0 version, please go to your plugins page and activate “Breadcrumb NavXT”. Also, deactivate “Breadcrumb NavXT 5.0 Migration Compatibility Layer” to make this message disappear.
To make this message disappear, navigate to the Plugins section of the WordPress admin. First, you will notice “Breadcrumb NavXT” in the list of plugins is not active, at this time you will want to activate it. Next, you will see a plugin named “Breadcrumb NavXT 5.0 Migration Compatibility Layer DO NOT ACTIVATE” deactivate this plugin.
Why is this Necessary?
In version 5.0, the file layout of Breadcrumb NavXT was reorganized. Due to this reorganization the plugin header information moved from breadcrumb_navxt_admin.php to breadcrumb-navxt.php. Additionally, breadcrumb_navxt_admin.php was removed from 5.0. Unfortunately, WordPress does not handle the change in plugin header location very nicely. Starting with 5.0.1, breadcrumb_navxt_admin.php was added back to the plugin, with a plugin header. However, this file now only exists to serve the notice to users about activating the plugin. Additionally, in Breadcrumb NavXT 5.2 this file will no longer be included with the release.
No, Really, Why is this Necessary?
Yes, the breadcrumb_navxt_admin.php file could automatically activate the new plugin file, and then deactivate itself. However, that sort of behavior is something plugins probably should not be doing, especially ones that are distributed from WordPress.org. So instead, the end user will have to intervene.
[end of transmission, stay tuned]