Java SE 7 update 21 displays mixed code security warning when a signed Java applet calls JavaScript code, or vice versa (which happens when NetDiagram runs client-side event handlers in JavaApplet mode):



Per Oracle's documentation, mixing the privileged signed applet code with JavaScript is now considered a security risk:
http://docs.oracle.com/javase/7/docs/technotes/guides/jweb/mixed_code.html

Updated NetDiagram assemblies that work around this by running the applet in sandbox mode are available for download from the clients area on our site, listed as version 5.0.1. The archive contains only new dll files, which can be copied over existing NetDiagram 5.0 installations.