Apparently you can’t use the Flex 3.x SDK to create custom components with the Xcelsius 2008 SP1 SDK — you must use the Flex 2.01 SDK. Maybe I just overlooked it, but I didn’t see anything in the Xcelsius SDK’s docs/tutorials that you said you must use the Flex 2.01 SDK, so I’ve been banging my head against my new desk wondering why my custom componets wouldn’t work…oh, and as a side note, the only way you know your custom components bomb is that they blow up Xcelsius, meaning most commonplace functions like File -> Open are disabled…no error messages, no warnings, nada…good stuff.
Since I didn’t see this info in the docs, I started googling issues and I ran across this blog post — Top 10 Xcelsius 2008 SDK FAQs — thanks for tip.