Notice: Object of class Piwik_Date to string conversion in

Just upgraded my Piwik from .5.5 to .6. I hit the UPGRADE button to update the database. I then log in to check my pages and this message comes up in all the boxes where graphs and charts should be:

Notice: Object of class Piwik_Date to string conversion in "/var/www/piwik" ...

What could this mean?

Please see http://dev.piwik.org/trac/attachment/ticket/1328/1328.patch

Wow! Thank you for your fast response. I made those changes and everything is fixed again. I hope this makes it into the official patch