You might need to set the --use-network=false compiler option.
Project - Properties - Flex Compiler
add --use-network=false to the "Additional compiler arguments:" section.
When deploying to a live server you probably have to recompile with --use-network=true.
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Greg Lafrance - Flex 2 and 3 ACE certified
Flex / AIR Development, Training, and Support Services
I'm still getting the same issue after updating the compiler settings.
If it helps, I split my application into separate Flex and BlazeDS projects using the instructions on this page:
As a result the Flex html runs inside the http://localhost:9083/mycontext/* domain.
Figured it out. Stupid typos ("locahost" instead of "localhost").