Error con Ssqldatareader

Tengo un problema con este codigo:

Function Calc(ByVal i As Integer) As Double
Dim sqlReader As SqlDataReader
Dim cnn As New SqlConnection
Dim vFormula As Integer

OpenConnection(cnn)

Try
ExecuteSQLTransac(cnn, sqlReader, "Select fFormula From
tbl_Silo
Where fIDSilo = '" & i & "'")
sqlReader.Read()
If sqlReader.IsDBNull(0) = False Then
vFormula = sqlReader.GetInt32(0)
End If
Catch MiError As Exception
MsgBox(MiError.ToString)
End Try

sqlReader.Close()

CloseConnection(cnn)

Return vFormula

End Function

Cada vez que lo ejecuto, me aparece el siguiente error:
System.InvalidCastException: Specified cast is not valid