Hi Dan,
we've been trying your code here, but we couldn't find the problems you describe in your message.
I can successfully run the queens example (using both the Javasoft JDK and the Microsoft VM) in the library\ javall\Examples\java2pl directory, both as distributed and integrated into my program -- so I believe my general usage is alright.
Everything seems OK, but did you try using the JDK with your code? The VM is the only thing that can work differently in this case. We tested your code with the JDK 1.2.2 VM and it ran perfectly. We created the query and executed query(), nextSolution(), and terminate() on it; then we created another query to test the assertion, and everyting worked fine. Please, let us know if you have any problem trying this.
Finally, thank you for your comments about closing the PLConnection object. We have found them very interesting, and we will work on that.
Jesus & the Ciao Prolog Team