I chose to enable the "Administrator Pass Phrase" in the set-up and when I activated the plugin, it logged me out and I could not access the back end.
The solution was simple, either do not activate the "Administrator Pass Phrase" or if you choose to do so, then you can access your site through the address: http://yourjoomlasite/administrator/?osolPP='pass phrase you set'
This in itself is an exceptional additional security measure for any Joomla site.
Well done to the OSOLCaptcha developer. Thank you!
Here is looking forward to not getting any more SPAM through my contact page on my site.
The themes and engine choices are really good, though I have to admit that I did not select the 'highslide' engine, but the rest were just what anyone would be looking for.
Many thanks for this excellent extension!
10 out of 10 to the developer.