Using a parameter from another Dataset in Expression Dialog Box

I am trying to set the visibility of a row in a tablix. But for doing that, I need a property of another dataset. I tried to go in the Expression Dialog Box and choo开发者_C百科se one property of another dataset. It will display:

1 =First(Fields!DatasetPropertyName.Value, "Customer")

The "Fields!DatasetPropertyName.Value" part is underlined red. If I am trying to build there is an error like "expression expected". (I have a german version and trying to translate)

What is wrong there? How to get properties from another dataset in the Expression Dialog Box?

Thanks for answers

Jochen

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Why is there a "1" at the beginning of your expression? Is that a typo? It should just be:

=First(Fields!DatasetPropertyName.Value, "Customer")

... (starts with "=", no spaces before) assuming "Customer" is the name of the dataset where "DataSetPropertyName" is populated. Don't worry about the wavy red underline. I see that in a lot of my expressions, and the reports compile and run just fine as long as the expression is ok.