java: bad version number

got this when i tried running my newly complied java program:
Exception in thread "main" java.lang.UnsupportedClassVersionError: Bad version number in .class file

i checked my java compiler version:
# javac -version
javac 1.6.0_11

then i checked my java runtime version:
# java -version
java version "1.5.0_06"

toink!

remember to check and use correct/similar compiler and runtime versions.