You previously installed a copy of the Symantec Protection Engine
After upgrading to Java 7 Update 51 you are no longer able to launch the remote Symantec Protection Engine
You receive an an application error: "Unable to launch the application."
Improved security settings in the Java 7 client prohibit you from launching the Java application.
A hotfix is available for SPE 7.0.2. See TECH213129 (Related Article) for the details. This issue has already been fixed with SPE 184.108.40.206 and onward.
For SPE 7.0.0, and SPE 7.0.1, follow the workaround shown below.
At this point you can try launching the Scan Engine / Protection Engine console again.