You run into trouble with the experiment_resources table. I'll update the page when we figure out the right way to do this.
Sometimes when you are building your emulab, you get an experiment that cannot be terminated. In this case you need to go into the tbdb database and remove all references to it. Here are some of the tables in which an experiment appears (the field name is always eid). What you actually do is search the database using mysqldumo and grepping the output. Hopefully, you used a distinguishing name for the experiment. Then you remove rows from the listed tables with the criterion being equality with eid.