A way I've got around this is to create a view on DS2 which looks at the MG1 on DS1. Then I use this as my measure group object within...

If you're referring to multi values for a single parameter I've had the same problem.

I see that when you setup the default parameters for a report you can have multiple...

I have fixed the problem now, thanks.

It was to do with the 'impersonate the authenticated user...' checkbox on the cube data source.

OK, I'm a knob. All that needs to be done is.

SUM([Account].[Source Type].&[TypeA], [Measures].[MyValue])

Simple.

I worked it out for anyone that needs to know...

IIF(Dimension.Attribute.CurrentMember.Name = "MyValue", 100, 0)