While setting up the Clam Antivirus module for ClamAV on a current installation of Webmin 1.870, I have encountered this warning which prevents use of the Clam Antrivirus module.
WARNING: Please indicate the backup path in the module's configuration. The path must already exists on the system.
The clamav module isn't a core webmin module - you should ask it's author about this.
Oh crap I completely forgot. I'm sorry Jamie. Apologies for wasting your time.