I was so relieved to find this thread after breaking a customer’s store after doing exactly what Lisa did. I was frantically searching Google when I came across it. Just a little more information which I had to look up:
Login to your Magento installation via SSH or FTP and delete all subdirectories under var/cache directory
Do the same for var/minifycache, although they are files and not sub-folders in there and have pretty long names! I began to wish I had used FTP and not SSH!
It worked perfectly though and saved me hours of worry, so thanks!