If Symantec Protection Engine (SPE) 7.0.x or 7.5.x (version 7.0.3/7.5.1 onward) is installed using Java 1.8.x and you try to open SPE web console using an older version of Java (like 1.7U 05), it results in “Class not found exception” error.
Install or upgrade to the latest 32-bit Java version (Java 1.8.x).