Chris,
The imported file an object or a record format that is the same as the Vectorworks object names. Before you insert a lighting device, look at the names of the record formats and symbols in the resource browser, also look at the layer and class names. Look for Lighting Device or Lighting Position, then delete them.
If you don't find any use custom selection to look for an object named Lighting Device or Lighting Position.
The Label Legend Manager, Convert to Instrument and Accessory Insertion Tool, are all failing for the same reason, the name conflect with "Lighting Device".
If you don't find it let me know and I can post a script that should allow you to find and delete the name.