I had this problem as well with visualvm version 1.3.2-0ubuntu2. As a workaround I remove the empty directory /usr/lib/jvm/java-6-openjdk and created a symlink in it's place that points to /usr/lib/jvm/java-6-openjdk-amd64. It seems strange that the package openjdk-6-jdk would install an empty directory, maybe they forgot to make it a symlink?
I had this problem as well with visualvm version 1.3.2-0ubuntu2. As a workaround I remove the empty directory /usr/lib/ jvm/java- 6-openjdk and created a symlink in it's place that points to /usr/lib/ jvm/java- 6-openjdk- amd64. It seems strange that the package openjdk-6-jdk would install an empty directory, maybe they forgot to make it a symlink?