I was trying to access an ColdSpring generated remote facad from Flex this morning when I got this error. It worked just fine by calling CFINVOKE and by calling the CFC directly in the browser. From my flash/flex app it however did not work. I hit my head for several minutes before finding the utmost simple solution.

I have multiple CF instances and it turns out that I did not fully setup the current instance to my liking. So if you see this error, check to make sure that your use-mappings settings is set to true in your services-config.xml file. Flipping this switch resolved my issue.

<use-mappings>true</use-mappings>