I am new to Traders Studio. I added a custom indicator (cupandhandleplot) to my session chart and got an error message. Now I cannot get rid of that custom indicator. Please could you help?

That indicator draws on the chart. We did not have a way of removing text programmicly until version 2.6, which is in beta so when you remove the indicator the text stays. This will be fixed in this next release. You should be able to remove custom indicator which don't draw text to the chart.