If the 64 bit edition of java is installed (even if you also have the 32 bit version installed) openproj will fail to open, with an error that it can't open jvm.dll. Uninstalling the 64 bit java version solves the issue.
I am running the:
Java SE Runtime Enviroment (build 1.7.0_01-b08)
Java HotSpot 64-bit Server VM (build 21.1-b02, mixed mode).
I am not having the problem described in this issue.