Error executing child request for ChartImg.axd

We are using Asp.Net Chart Controls to create a series of charts from a csv data stream that a user uploads to the server. Until we hit this error "Error executing child request for ChartImg.axd." Since uploading the file is a post-back, we had to change the charting HTTPHandlers.

The solution: open the 'web.config' file, find the line
<add path="ChartImg.axd" verb="GET,HEAD" ...
and add a "POST" verb:
<add path="ChartImg.axd" verb="GET,HEAD,POST" .....