I'm getting the same effect with a simple stepped line chart, no actions specified...

I can change the chart type to a regular line or column and it works fine, but when I set it to stepped line, then a mouse over on the chart region throws the "Parameter is not valid" message. Clicking on the message causes the chart to disappear.

It happens in preview mode with both Report Builder 3.0 and SSBI Development Studio.

The data is clean. Perplexing.