It is hard to say without debugging the page directly.
Start by taking that sql statement and running it in your database directly. That will be the easiest way to make adjustments and make sure you are getting the data you need.
I didn't know what database you were using, so my syntax could be wrong for your database type... once you have your SQL statement worked out, if you still have problems you should try browsing the page referenced "DynamicWebCharts/Data/diagramm_dataparser.asp?" directly. When it shows the page name like that it means that page has an error. By viewing the page you can find out more about the precise error.
If you want Webassist to help directly you would have to sign up for a paid phone support incident. That would allow us to connect to your computer and debug the problem with you directly.
