The solid study line becomes dashed when there is not enough data loaded on the chart to properly display the study period. For example, you have a Moving Average study and the period is 200 on your chart, but you see a dashed line on the left of the chart. In this case, you can click on the left edge of the chart. The cursor will become a left-facing arrow and you will be able to load more data. You can then zoom back in with the + and – and the line will show solid.