Can’t access admin area after upgrading to Magento 1.4?

Me neither. Well, I can now after a manual fix.

The upgrade via MagentoConnect seemed to run successfully, but I immediately got a server 500 error when trying to access front and backend. *Sigh*. I reset all file permissions, and cleared cache folders (/var/cache and /var/session). The front end worked then, but no back end.

I was a little surprised by a problem like this, given that Varien had bowed to much open source public pressure to tighten up its release process to ensure that ‘stable’ releases were in fact stable. It was evident that nearly every man and his dog would immediately run an upgrade on their production website every time a .1.1 release was put out without testing first.  I felt for them!

I had expected therefore that the dev site that I had installed on a shared host we use for ourselves and clients would upgrade to Magento 1.4 CE via MagentoConnect smoothly…