I could not find a reliable way to avoid the file-locking issue. I minimized the scope of the Model and Validator objects and this seems to have mitigated the problem somewhat but it hasn't gone away completely. I added some exception handling to catch the exception that is thrown warning the user that they need to restart the Widget.
I ran into a similar problem in the Replicator where I try to instantiate the ecoregionsmap when running the scenario shortly after instantiating it to validate the scenario. There is a file lock on ecoregions.gis. Again, I added some exception handling. If I get any suggestions on the Developer forum, I will try to implement them. I can't think of any solutions that don't involve modifying the Core code which I don't want to do.
I released a new version of the Widgets for testing by Rob and his team.