I can't open version 18 any more since the free trial has run out. I kept thinking I would have my drawings complete before the trial was up but kept running into things that almost worked (close enough to keep me trying again and again.) Hindsight shows clearly that I should have checked out the conversion before investing so much time into trying to complete it in version 18.
The final problems I encountered were that I couldn't get the wall top modification to work (more than the one time it did while my graphic was messed up.)
Before that, I was placing a 3x3 array of picture windows in a 17 foot first story wall over a basement. I had a number of named workplanes defined including "Basement ceiling" and "First floor." The windows were all supposed to be placed on the First floor workplane but some of them insisted on being placed on the Basement ceiling workplane instead. I tried re-placing the windows with the proper workplane active, moving them to the correct workplane, reloading the file, reloading the program etc. Nothing I tried put the windows where I wanted them. I finally adjusted the height of the sills to have them appear where they belonged. My basis for trying to make things work the way they should is to avoid the "house of card effect" that occurs when one starts propping things up to make them work.
I found myself repeatedly closing and reopening my project or even reloading the program. Sometimes it worked but often it didn't. It is probably a good thing that the trial ran out so that I don't waste any more time trying to use it. It will be interesting to see if version 15.2 is more reliable.
Thanks for your interest,