Hello Vahid,
What is the data type for the X
axis - are you using Date Time or String values?
You should be able to switch the Smooth
Line - Sub Type to: XY Scatter. Then in the Values Grouping Editor, you need to pass the X value (for example: =Fields!Date.Value).
From the Chart Areas ->
Axes -> Primary X -> Scale tab, from Numeric tab, you can choose Date Time sub type and you can configure the formatting. You can check some of the report examples shipped with the installation (for example: CalculatedSeries_PolynomialRegression.rdl).
Hopefully this helps. Let us know if you have any questions or if you need assistance.
Best Regards,
Nevron Support Team