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Had a troublesome error. I moved my development environment in Eclipse to my laptop. Imported the project. Everything went smoothly. Started the server. All fine. The minute that I had to go to the database, it blew up with an error that looked like this:
javax.servlet.ServletException: java.lang.UnsupportedClassVersionError Unsupported major.minor version 51.0
I realized that my new Eclipse Juno was set to compile for the 1.7 Java environment and Tomcat was running 1.6 Java JRE.
I went into the project properties, and selected Java Compiler option. On the upper right corner there is a link where you can click to Configure workspace settings. The JDK compliance is set to 1.7. (which is version 51). Use the combo box to set it to 1.6 which is version 50 and it should work.