I\'ve looked high and low and can\'t seem to find an answer to what appears to be quite a straightforward issues (I would think).
I have a line chart where there is
Solution
Just put your Fields!(YourSeriesGroup).Value in Series Groups to above of Fields!(YourCategoryGroup).Value in Category Groups, your series group should be in both Series Groups and Category Groups (should be above of your initial category group).
And after that right click horizontal axis and select Horizontal Axis Properties. Set Axis Type to Scalar and click OK.
Result