These errors usually appear because some core modules are missing, or not have the same version number as the latest release. When doing an upgrade, sometimes not all the required modules are upgraded.
To fix it, you need to force an upgrade or install of the missing modules. To do so, you need SSH access.
Run the following command from your Magento root directory.
./pear install magento-core/Mage_All_Latest
You should see some errors about required modules having the incorrect version, e.g. “magento-core/Mage_Core_Modules” or “magento-core/Mage_Core_Adminhtml”. For each of the missing modules, run this command:
./pear install -f module_name
for example to force an upgrade of Mage_Core_Adminhtml, you enter this:
./pear install -f magento-core/Mage_Core_Adminhtml
You need to include the ‘-f’ flag (force), or else PEAR will ignore the module if an earlier version already exists.
When all the missing modules have been re-installed, run this:
./pear install -f magento-core/Mage_All_Latest
It should complete without errors, and hopefully your problem will be solved.
Almost all issues related to Magento Connect and upgrades can be solved this way.