After spending hours on different forums to find the solution to this problem, I was finally able to work through it using this page (drupal.org/node/360836). The difference between that article and this is that I changed the word 'variable' to 'dr_variable' to match my SQL table names.
1. Go into the PHPMyAdmin dashboard and navigated to the database I wanted to clear.
2. Click on SQL tab and entered the following:
SELECT * FROM dr_variable WHERE name like "cron%"
3. Disabled all non-core modules.
drush pml --no-core --type=module --status=enabled --pipe | xargs drush -y dis
4. Re-enabling the modules one at a time to find which was causing the cron error was the biggest time consumer. Going down the list and running cron after each module allowed me to find that the Backup and Migrate module was the source of the cron error. Thus I disabled the module, cleared the cache twice and then was able to run cron successfully.