You get the following error when calling a reporting services report from your ASP.Net web application that passes a parameter on Non-IE browsers using the 2010 ReportViewer control:
Missing URL parameter: IterationId
Sometimes this error will occur when you use the line control on a report. The Line control tries to include a standard blank image right after it, but the URL is missing that parameter in FireFox and Chrome. Try removing the line control from your report to see if the error disappears.
This error does not happen with IE Browsers. Just ignore.