That error will be thrown if SlickEdit has detected that the location specified for JDK 1.6 is not valid. I can see that it will attempt to validate the install by finding a javac, a java executable which is version 1.6 or later, and a JVM lib (ie. jvm.dll, libjvm.so, etc.) which is required for SlickEdit's Java Live Errors.
Now, I am not currently in the office so I don't have access to a Mac at this moment, but do those components exist at "/Library/Java/JavaVirtualMachines/1.6.0_30-b12-404.jdk/Contents/Home/" ? If not, do they exist somewhere else under your Mac JDK 1.6 installation? If there is something going haywire here for configuring Java Live Errors on Macs we will work to get it fixed ASAP...but hopefully this helps.