When you upgrade your Magento to 1.4 then some strange stuff can happen.
First read the upgrade notes.
Secondly a note about .htaccess files that Magento 1.4.0.1 installs. For example Estonian hosting provider Zone does not support php directives in the .htaccess files.
If you get ”
Internal Server Error
” or similar after upgrade using Magento Connect then check your .htaccess file in / folder. Very likely Magento upgrade has overwritten it and the php directives are there. Comment those out if these are not supported by your hosting provider.
Refresh the page and it should work. Voila!:)
If javascript does not work or product image uploads fail, then be sure to check .htaccess file in media folder. So open .htaccess form media folder and comment out all directives from there.
If you see something like “Exception during cache and session cleaning: Invalid mode for clean() method” then remove app/code/core/Zend/Cache/Backend folder.
After you’re back in the admin of 1.4.0.1 be sure to flush and refresh all indexes and cache. Don’t enable any caching at this point yet.
