After upgrading to the latest version of BlueCoat ProxySG, attempts to download the BlueCoat Web Filter failed.

Building database     Reading App Filter       ERROR: No regex table ready (1 – size -605820752)
ERROR: App Filter Read FAILED

I couldn’t find anything in the BlueCoat knowledgebase.    I figured I needed to delete the Web Filter database and do a fresh download.   The question was how to do this.  For that I ended up in the Bing cache for the BlueCoat forum.

First, under Configuration, Content-Filtering, General, Uncheck BlueCoat.
You can’t have the database in use when you try to purge it.   Once you uncheck this, people aren’t filtered.

Next SSH to the proxySG, go into enable.   The type the following each on its own command line

Config t
Content-filter
BlueCoat
Purge

Back in the web gui, initiate a new BCWF download.   When that succeeds, re-enable the BlueCoat filter that you disabled earlier.