This is a general troubleshooting page and will hopefully cover all potential problems you may encounter.
The DTM Editor a Simba Extension. See Simba Extensions for more information on extensions and how to enable the DTM editor.
All extensions are in the Extensions folder. If this folder is empty, you may need to manually download the Extensions or reinstall Simba.
This means your settings.xml has become corrupt somehow, or Simba may not be able to create it. If a settings.xml exists in your Simba directory, you can delete it. (All your settings will be lost, but this shouldn’t be a bug deal)
There is a bug report pending on this issue.