When launching the Screencast tool I receive a message "Application Blocked by Java Security" When I try to launch the Screencast tool in Droid Explorer I am presented with this dialog.
Disclaimer: I am the lead developer of Droid Explorer

The Screencast application is out of the control of Droid Explorer development team as it is a 3rd party project. The project actually seems like it has been abandoned.

I found a fork of the code on Github that looks like it is under more active development: https://github.com/xSAVIKx/AndroidScreencast



The workaround to get it working is only a few steps:


Open the Java Control Panel (Located in the Windows Control Panel) 

Next click the Security Tab and Click on Edit Site List...

Click Add and enter http://androidscreencast.googlecode.com/svn/trunk/AndroidScreencast/dist/androidscreencast.jnlp (This may change in the future for the github fork)

Click OK
Click Continue
Click OK to close the Java Security Control Panel



  Note: When you launch the Screencast plugin again, you will be
  presented with a warning because the application is not signed by the
  developer.