java.security.AccessControlException: access denied (java.net.SocketPermission 127.0.0.1:8081 connect,resolve) - main reasons

Question

What are the main reasons that cause the exception reported?

Same trusted signed applet (Digicert certificate), works great on some PCs, doesn't work on other. Exception occurs when i try to get an attachment stream through URLConnection

Where it doesn't works, i resolve with

grant { 
    permission java.security.AllPermission; 
};

in

java.policy

but i would like to avoid to update every PC.

Could be a port (8081) issue? What should I investigate?

Answer 1

Same trusted signed applet (Digicert certificate), works great on some PCs, doesn't work on other.

It isn't trusted by those other PCs, and wasn't accepted by the user as trusted when asked.

OR

This is my manifest.mf

Trusted-Library: true
Application-Name: MyApp
Name: MyName
Permissions: all-permissions
Created-By: 1.6.0_16 (Sun Microsystems Inc.)
Caller-Allowable-Codebase: *
Main-Class: MyClass
Codebase: *

If that's the complete manifest, this JAR isn't signed at all, let alone by a trusted certificate. It should be full of Name: and SHA-256-Digest entries.