I was recently playing about with hiding the All member for several dimension attributes in my SSAS project. In order to hide the All member we set the IsAggregatable property to False. This immediately had the effect of my queries not returning any results. In hindsight my problem should have been blindingly obvious.

When we no longer aggregate the members on a dimension attribute, SSAS does not know what member/members to use unless you tell it explcitly, or set the DefaultMember attribute. Doing one or the other will stop your measures and calculations from vanishing.