erwin DM is setting my models to Read Only. I am logged into Windows 10 as a Windows Administrator user but when I go to save my model changes erwin complains the file is read-only and cannot do so.
It is most likely because of the model in question. If a model has any issue(s), the current model is marked as 'Read Only' during save and the changed model is saved as xxx.erwin1 (notice the number appended in the file extension). To check it you can try it with a new model, add a couple of objects and then try saving it. It should save with no problem. Open that model, make yet some more changes and save it again. The save should work as expected.
This functionality of marking a model as 'Read Only' is offered by Windows and erwin DM takes advantage of that to alert the users that the model they saved may need to be looked into or 'cleaned up'. If it is happening consistently with a specific model, please contact support for the model to be looked into.