I just took a flex application that is going to be used by multiple products (its a flex based portal), and needed to move the core code into a swc, once I created my swc I kept getting this weird error :
Inconsistant linkage in D:\projects\clients\someClient\someProject\trunk\3rdPartyLibs\swc\playerglobal.swc(Object) - 'isNaN' is marked as extern, but '__AS3__.vec:Vector$int' is not.
I did a google and found a couple of references :
http://www.mail-archive.com/flexcoders@yahoogroups.com/msg122106.html
so I went back to my application project to see if I had any special compiler settings, and remembered I had :
-target-player=10
I added that to the Additional Compiler Arguments in the Properties | Flex Library Compiler panel and its now works.
Hopefully this will save you some discovery.