report item not linked to dataset

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C#3.5

SSRS

RDLC

Hi frinds,

I try to design the rdlc form body with datatset.what i have done so far,

1.I created the Dataset1 using reportwizard.
2. if i connect the all the fields in the Dataset1 using tablix or table, then there is no porblem with data.

But i drag the field from Dataset1 to the rdlc form body, It's expression show as following:

=First(Fields!RegistrationDate.Value, "DataSet1")

with red underline on this line.
what is the problem in this condition is when i click the filed in expressin category, it show the meesage like report item not linked to a dataset.


what is the problem?