If you have the daily build of Chromium installed but you want to downgrade to the stable build, this blog post may help you out.
1: Open up the Synaptic Package Manager and type in chromium-browser.
2: Right click on chromium-browser then click on Mark for Complete Removal.
3: Click on Apply. Wait for Chromium in uninstall.
4: Click on chromium-browser then Package on the Menu Bar then click on Force Version... Choose the version you want to install Eg. (your ubuntu version-updates) then click on Force Version then click Apply.
5: After Chromium is back installed, run this command in the Terminal to delete your old user data profile (Not as Super-user!) rm -f './.config/chromium/Default/Web Data'
6: The stable build of Chromium should now be install and work without any errors.