An error occurred during upgrade (2.15.0)

On October 21st, I upgraded PIWIK to the most recent version, 2.15.0 and I received the following:

An error occurred:
Variable “enableMeasurePiwikForSiteId” does not exist in “_piwikTag.twig” at line 3

To be honest I can’t remember if I upgraded through my PIWIK Dashboard, or through Softaculous via my cPanel… I do remember though that it said before I upgraded that it was a “different” version that needed to be upgraded rather than the version it said on the page… the left hand didn’t understand what the right hand was doing… so I guessing that somewhere in there is where the glitch occurred and caused this error!

I can NOT access my PIWIK account, what can I do to fix this?

Looking forward to your reply,
Blaine Klingaman

Can you try re-upload all files? looks like some files were not successfully overwritten by upgrade?