Converting Date String To DateTime Format Vb.net?

I have this example and it gives me exception "Conversion from string x to dateTime is invalid"

here is my method to validate Datetime.

Example Date string : "27/03/1985"

Public Function validateDateColumn(ByRef FieldName As String) As Boolean

Try
If IsDate(FieldName) Then
Dim actualDate As DateTime = CDate(FieldName)
Dim DtLicExp As DateTime = CDate(actualDate.ToString("d", Thread.CurrentThread.CurrentCulture))
FieldName = DtLicExp.ToString("MM/dd/yyyy")
Return True
End If
Catch ex As Exception
'FieldName &= "Format must be MM/dd/yyyy"
Return False
End Try
End Function

validate this date string formate to datetime.

I want to convert this date "27/03/1985" to datetime.