I am running Spark under JDK1.6 and it works okie.
Java™ SE Runtime Environment (build 1.6.0-rc-b91)
I do get that same error that you get when Running Spark on my Dual Monitor computer.
It is an error from X server.
But I only have gotten with the Dual Monitors.
With the way Derek has focused on Spark, it would be VERY easy to convert to handle JDK1.6 perfectly. There are few things that would need to be done for support under Linux though, especially with the latest version of Gnome.
JDK1.6 has lots of bugs still with Gnome version 2.14.x