Possible solution from this thread, although it's regarding Away3D and not Pv3D, it's still relevant.
http://groups.google.com/group/away3d-dev/browse_thread/thread/9bf349c37aab279a"various way to fix it have been noted: try typing the full import to arcane
(presume you've already tried this). try clearing your aso files in cs3 (i
assume your using cs3 as i've not heard of this occurring anywhere else),
try inserting a return character before the namespace reference (my personal
favorite :D) - these thing have all 'apparantly' fixed the compile error in
the past. I find no documented reference to this problem in the adobe
bugtracker which is strange - clearly the code is correct but something is
going wrong in the compiler execution. might post one myself"