MACROMEDIA FLASH 8-LEARNING ACTIONSCRIPT 2.0 IN FLASH Manual page 709

If the called file is published for Flash Player 6 and you want to port the called file to Flash
Player 7, include or
System.security.allowInsecureDomain
in the called file, using exact domain-name
LocalConnection.allowInsecureDomain
matching, as shown in the code examples earlier in this section.
If the called file is published for Flash Player 5 or earlier, and both files are not in the same
domain, you can do one of two things. You can either port the called file to Flash Player 6
and add or change a statement, using exact domain-
System.security.allowDomain
name matching, as shown in the code examples earlier in this section, or you can port the
called file to Flash Player 7, and include a
System.security.allowInsecureDomain
statement in the called file, using exact domain-name matching, as shown in the code
examples earlier in this section.
HTTP to HTTPS protocol access between SWF files 709