MySql : " Warning: MySQL server has gone away "
When attempting to log-in to a Drupal website I encountered this error, and couldn't log-in. Bit of a headache, in my case I solved the problem by loading up phpmyadmin, going into the variables table and deleting 'cron_last' & 'cron_semaphore'. I then went into the system table and disabled dblog, poormanscron, search and update modules.
This has solved the problem, I'm not exatly sure what the problem is though. This article on d.o indicates it's to do with performance: http://drupal.org/node/259580