Why the tablet is undisolved after washing?

I'm having problems with my Bosch dishwasher, since yesterday the washing tablet got stuck undisolved in its compartment after the normal washing cycle. I did dry the compartment before putting the tablet and have tried three different makes of tablets (which have been successful in the past). Every time after the washing cycle the tablets were there undisolved. Have checked the filter, tried different washing cycle but the problem persists. The dishwasher is just over one year old.