Thanks so much guys. I'm sure there is a lot of clean up that had to be done, and I have no doubt my large 530 MB file probably needs a LOT of clean up as well. I just don't know enough on how to smoke out those problems and how to do it.

I did experiment with it further and found the problem. There are way too many points in the curves. My intention was to pull it down five feet, scale the bottom face down some, rotate it some, and then repeat to create the bottom of the cave structure, but the program absolutely wouldn't tolerate that. Whenever I try to do any kind of maneuver on it such as scale, intersect faces, rotate, etc., that's when it shuts down. I got around it by pulling it down into a solid 5 feet down (It would allow that) and then on the bottom edge I started combining the points into a much more simplified pattern, which of course is a cruder representation of the curves, but for my purposes is sufficient. The cruder curves had only about 10% of the points the original curves had and as long as I worked with those points and left the original curve alone, the program wouldn't shut down. I could pull down further and work with that to create my cave structure. It seems that for any individual operation, if the number of points and/or faces exceeds a certain number, the program will shut down. Coding-wise, it acts like an informational storage stack problem.

I'll take a look at the files you guys posted and see how I can use those. Thanks so much guys. Much appreciated.

Bad geometry....That may be the answer. The file does close down suddenly on its own. It has nothing to do with the larger file. It does not come from any other file format. It is created solely using SU 2017. What I am doing here is creating a lake within a cave with islands in it. To simulate a cave, I push/pull it down about 10 feet and then use SCALE to reduce the lower outline centrally (with SHIFT) along with some other maneuvers (rotate, move, etc.). Once I am finshed with that level, I repeat the process of push/pull every ten feet until I can close off the bottom of the cave. Then I repeat the process in the other ditection to get the top of the cave. But it crashes every time I start to anything with it in this manner. I've used this method of creating a cave successfully without a problem before, but this is the largest one and most complex by far I have tried. Maybe it's too much geometry and I'm overloading the stack or something.

Lake Realm Outline Start.skp

I use SU 2017 as a subscription doesn't make sense as I don't use the program regularly. I have been working on a file that is huge, 530 MB, and have been doing fine. I am now working on a file that is to be added to it, but it only about 3 MB in size. The problem I have is that I cannot do anything with it. Anytime I try to do a cut and paste or other action that increases or adds to it, it suddenly crashes. There is no Bugsplat. It simply just closes. I have no idea why. I've tried several workarounds such as making the added part a compenent then exploding it, but it still crashes. I've tried just adding the outline of the lines, trying to get that and manually add in the planes one by one. It still crashes. It doesn't do this on any other files except this particular one. I run two different computers which are more than enough to handle this thing. One computer has an RTX 2060 super video card. The driver is updated. I turned off the extensions on SU. I've purged the unneeded files (There weren't any! It was that simple a file. It's so small I don't even have to use compenents in it.) The program still crashed! I switched over to my monster computer for Video work (TUF GAMING Z690 D4 plus WIFI with i9-12900K CPU and RTX 3080ti video card on Thunderbolt). Video card driver is updated. Extensions turned off. Files purged. It does exactly the same thing. It crashes if I barely try to do anything with this little file.
Does anyone have any idea what is going on here?