Something that you don't address is the importance is once copy and paste the file you have to right click the family and go to property and uncheck read only. Once you do this step you can save the family w/out any problem.
Another thing. I my case I am working on imperial and to make work I had to modify the template in "MM". For ex. I made a 8" thick I had to convert to "MM" 203..2. this'd was the only way it would work. Don't try changing the units in the template it will nor work. It will give an error on the width of the Hollo Core slab.
All my templates work once I did all this changes 8" to 203.2 mm, 10" to 254 mm, 12" to 304.8. what I am trying to say is the template need to be in "mm" in order to work in imperial.
