Examples of such issue:

 javax.servlet.ServletException:
com.caucho.jsp.JspParseException: _jsp/_logon__jsp.java:10: cannot
access org.agnitas.beans.EmmLayout
bad class file:
/home/mvohra/openemm/webapps/core/WEB-INF/classes/org/agnitas/beans/EmmLayout.class
class
file has wrong version 50.0, should be 49.0
Please remove or make sure it appears in the correct subdirectory of the
classpath.
import org.agnitas.beans.EmmLayout;
^
1 error

This normally happens due to mismatch between your Runtime Java version and a certain library that was probably compiled with an older version of java.<!>

Solution

These types of bad class version errors are caused by a Java version mismatch between the compiled proxies and your run-time. Either try to change the Java version that you are running or try to find pre-compiled java libraries (where this error is occurring) that were compiled with the java version with which you are running the app.

Below are a list of some of the version numbers and their corresponding Java run-times, they should help you to determine that the classes with the libarary were compiled with what java version.

Version 50.0 = Java 1.6.x
Version 49.0 = Java 1.5.x
Version 48.0 = Java 1.4.x