ck - Thanks for your suggestion. We had noticed it felt rough inside the salt reservoir and the salt indicator had ceased to indicate "empty". The left side panel of the dishwasher was removed and it was possible to see through the transluscent plastic salt reservoir a clogged container 3/4 full of hardened salt. Removal of the softener unit was not easy. The unit had to be layed on its right side so that the base could be unscrewed to allow access and removal of the softener unit. The solid mass of hardened salt took some effort to chop out. We are happy to say the dishwasher is now working properly again.
Derek
January 2009