I don't know how Dr. Java is configured, but I suspect there's a version mismatch with the compiler (javac) and execution (java) executables. Drop to a console and type both:
and ensure the results match. Report the results here if you need to.
If the results do match, then dig into the Dr. Java configuration and ensure that both the compiler and execution settings point to the same Java installation. If they don't match, then you have multiple Java installations with paths or environment variables pointing to both, one for JRE and one for JDK, that you need to fix so that both point to the same Java installation.