You attempt to query a member of a dimension but get the error “Dimension contains more than one hierarchy, therefore the hierarchy must be explicitly specified”.
This can happen when you don’t properly qualify a measure or dimension e.g. you specify [MeasureName] instead of Measures.[MeasureName] or you attempt to refer to a dimension attribute via [Dimension].Currentmember instead of [Dimension].[Hierarchy].CurrentMember – Checking all of your Calculations is likely to reveal the culprit.