Plugin 'nb' is not activated

Piwik v2.2.0 monitoring a WordPress blog (v3.8.2 using WP-Piwik v0.9.9.8). Stats seemed to be working (but not in agreement with Jetpack which is a separate issue) and have now stopped with the following error:

Error: The report ‘nb_pageviews’ was requested but it is not available at this stage. (Plugin ‘nb’ is not activated.)

Can anyone shed some light on what this error message is and how to correct the issue?

Much appreciated!

Re-activating and re-installing the WP Piwik plugin makes no difference.

Does anyone know what “plugin nb is not activated” in the error message is referring to???

OK, I finally found the work-around to this bug. Apparently if you add data lines to the “Visits Overview (with graph)” Piwik dashboard widget this bug is triggered. The “nb” plugin is apparently a core plugin. Deleting the “Visits Overview (with graph)” Piwik dashboard widget and re-activating is the “fix”. This bug is documented here: