After some playing about, and discussion with the CoinIMP developers, got some conclusions. The sites where the site-specific code is added manually to the HTML work OK; this can be seen at zami.co.uk and kank.co.uk. I also added the general code - which isn't site-specific - to chadds.co.uk, which also appears to work OK although it is harder to know this for sure as it isn't site-specific. However, I have added the Joomla module to several Joomla sites, none of which appear to show up or work; on cybertrax.net the warning message shows but it either does not appear to mine, or else it isn't feeding back statistics to CoinIMP. I have also added the module to the following sites; greetland.net, ashasworld.com, dazzax.com - all with the same non-effect.
Is it possible that the module needs updating due to the recent fork in the currency?