refer to: http://helpx.adobe.com/flash-player/kb/flash-builder-flash-player-throws.html

Error message: SecurityError: Error #2148: SWF file C:/Documents and Settings/Administrator/Adobe Flash Builder 4/domain_mgr_flex/bin – debug/domain_mgr_main. SWF cannot access the local resources C:/Documents and Settings/Administrator/Adobe Flash Builder 4/domain_mgr_flex/bin – debug/textLayout_4 0.0.10485. SWF. Only file system-limited SWF files and trusted local SWF files can access local resources.
at flash.net: : URLStream/load ()
at flash.net: : the URLLoader/load ()

the solution:
in the C: \ WINDOWS \ system32 \ Macromed \ Flash \ FlashPlayerTrust directory (if FlashPlayerTrust directory does not exist, can create a) add a file, such as: True.txt (file name can be anything from), C:\Documents and Settings\Administrator\Adobe Flash Builder 4\ Flex workspace path, of course, can also be set to C:\

or all the disc characters can be written:

C:\
D:\
E:\
F:\
Note: You will need to restart your browser after editing this trust.txt file.
Originally, I had FlashBuilder4.0 installed on my machine, so I didn’t have this problem when debugging SWF. FlashBuilder4.7 was installed later, but version 4.0 was not uninstalled, so running SWF in the 4.0 compiler will report this error, while version 4.7 will not, presumably due to workspace path conflicts.
Strangely, errors are only reported in Firefox, but not in IE. It seems that the Flashplayer of these two browsers is quite different.