Go to Chart Wizard and select the line. Delete Series 3 when the Source Data dialog comes up.
For Series 1, change Values to the MaxValue column (=Sheet1!R2C2:R4C2) and The Category (X) axis labels (bottom field) to the Date column (=Sheet1!R2C1:R4C1).
For Series 2, do the same with MinValue.
Make sure to add their names in the Name field.
UPDATE: Hmmm, I missed the VB.net in the subject only.
Try
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