Magento

Please help! After upgrading several modules i got a failure message:

Warning: include(Mage/Core/Model/Mysql4/Helper/Mysql4.php) [function.include]: failed to open stream: No such file or directory in /home/basta/domains/bastakinderkleding.nl/public_html/lib/Varien/Autoload.php on line 93

2011-08-26T08:49:23+00:00 ERR (3): Warning: include() [function.include]: Failed opening ‘Mage/Core/Model/Mysql4/Helper/Mysql4.php’ for inclusion (include_path=’/home/basta/domains/bastakinderkleding.nl/public_html/app/code/local:/home/basta/domains/bastakinderkleding.nl/public_html/app/code/community:/home/basta/domains/bastakinderkleding.nl/public_html/app/code/core:/home/basta/domains/bastakinderkleding.nl/public_html/lib:.:/usr/local/lib/php’) in /home/basta/domains/bastakinderkleding.nl/public_html/lib/Varien/Autoload.php on line 93

Already an answer on this? I have the same error after upgrading to 1.6

Same problem here....I got my site back by deleting the var/cache & var/session folders

Delete the <magento-dir>/var/cache folder