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This one is a doozy. I hope it gets fixed by a hot fix rather than the next "dot" update. Bjorn Jensen gets credit for finding it. I ran into it myself yesterday when working on my blog entry. If you have a CFC that returns numeric data and uses a returnType of numeric, then ColdFusion will throw an error. Here is one example of code that will throw the error:
<cffunction name="getX" access="remote" returntype="numeric"> <cfargument name="id" type="any"> <cfreturn arguments.id> </cffunction>
I then entered this URL to test: http://localhost/test.cfc?method=getx&id=1&returnformat=json. The error was:
java.lang.Double cannot be cast to java.lang.String
The fix is to simply change the returnType to string (or any). You can find more detail (and vote for a fix!) at the public bug tracker: http://cfbugs.adobe.com/cfbugreport/flexbugui/cfbugtracker/main.html#bugId=80375.