When you go into the Purge dialog and you see STB styles listed under the tab for items you cannot purge and want to get rid of them
This problem is usually caused by blocks that were created in STB drawings that are inserted into your drawing.
Follow this process to get rid of them:
1. Open the Drawing
2. Type in CONVERTCTB and select monochrome.ctb and click OK
3. Name the new STB Converter and click Save
4. Type in CONVERTPSTYLES and select the Converter.stb
What we are doing is creating a mapping from CTB to STB that can be reused for any other drawings, so we have to do this only once.
5. Now we launch the Plot Dialog (model or paperspace doesn't matter for this step) and we select New to create a new STB
6. This will launch the wizard, so we set the dialog screens per the below screen shots