Hi Jonas,
I assume you encountered this problem after dragging and dropping a ChartWebControl on the WebForm. You should not have encountered any problems with the samples that shipped with Essential Studio install.
The reason the samples work but not a new application is because the VS.NET Designer does not add the lines attached with this forum for the other assemblies that are referenced.
You can either copy the Register tags from any of our samples or can copy from the attached file.
Do not hesitate to contact us if you have any further questions.
Regards
A.Sivakumar
ChartReferences.zip