Passing Data Through Forms

I know there are other threads on this but I have tried all the solutions and none have worked.

I currently have 2 forms, a customer form and a customer health form.

I want to pass the membershipNo from the customer form to a newly opened customer health form.

this is the code I am using but it isnt working, actually it is, but when i delete all the current customer entries and enter new ones it doesnt pick up the details and all the controls on the customer health form are greyed out.

Code:

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Private Sub cmdCustHealth_Click()

DoCmd.OpenForm "CustomerHealth", , , "[MembershipNo] = " & Forms!CustomerForm!membershipNo, , acDialog

End Sub

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The control source on the text box on the customer health form is "membershipNo" where am I Going wrong?

Access VBA question moved to Office Development