When I look at Statistics Window - all looks okay but SpamSieve Accuracy just show zero for 100% accuracy which I know is not correct.
How do I fix?
Most likely, it is correct: SpamSieve filtered zero messages because it isn’t setup properly. Please check the log.
Okay I will try & keep an eye on this. Another question I cannot open log from the spamsieve window. I presume I should be able to do so but get following message;
Unable to read the dictionary of the application or extension because it is not scriptable
Spamsieve is generally working well I just seem to have a couple of gremlins in the system. 
It sounds like your Launch Services database is messed up so that the OS is trying to open the log file with an inappropriate application. Please try using the Open Log command instead of Edit Log, or install TextWrangler.