TransferLog server hostname

I am transferring an apache configuration from an old box to a new one
which is using Apache 2.

I am having trouble with the line
TransferLog "|/usr/local/bin/cronolog /www/servers/logs/site_logs/
`hostname`-site-%Y%m%d-1.log"

Previously this would generate logfiles with names which included the
server hostname. For example thehost-site-20080422-1.log
But on the new box I am getting names such as:
`hostname`-site-20080422-1.log

Any ideas?