At first you should check major version of compiled problematic .class
file, in your case map/CareMonths
. See this answer how to do it.
WAS7 uses Java 6 (as said Jacek), and Java 6 uses major version 50, so you have to compile your project with Java 6. How to set proper version of Java compiler depends on your IDE (e.g. Eclipse, IntelliJ) or build tool (e.g. Maven, Ant).