Well, at least when you’re using flash + amf. Last week I was getting the dreaded NetConnection.Call.BadVersion error every other day. Debugging blindly, I had no way of knowing whether I was moving towards or away from the solution. On the verge of giving up until I gave Service Capture a try. The handy tool sets up itself as the proxy to your browser and monitors all kinds of traffic, SOAP, XML, Text, JSON, Flash Traces, you name it. For my case, I used it primarily to decode the AMF responses from my zend_Amf gateway. It decodes the binary responses and place it along the request and response headers in a familiar object tree view, making inspection a breeze.
And I also realized what was causing the errors: the flash player was trying to decode a redirection to facebook’s login page as Amf. Doh.