You're not alone in this, damainman at all. I regularly have those display issues and at times get the hicon error you posted in the op. My C2 failures almost always happen after running a preview (or export) of the game. Any subsequent preview (if I can get one to work at all) will have all text tiny and missing values and the C2 IDE is largely unresponsive and throws errors left and right.
Ashley if it is indeed linked with a need for windows to show icons, would it be possible to add a text-only option for projects that intend to be large? I've done some toying and I can increase how many successful previews I can achieve by having the object and property bars closed, saving, restarting, and previewing from there so those things don't have to load. It also did help a little to split up my biggest event sheet (500 events down to 2x250).
I'm not being wasteful or poorly planning Courier. I could probably reduce the object count by around 50 or 60 if I really tried, but the project is at 1,200 objects by my best count. About half of it comes from Spriter and how many NPCs I have in the game (and all the objects created for it). My events aren't crazy--for the whole project I'm at 2,600 events split up across a bunch of event sheets. It's as efficient as I can make a large, varied RPG. It never reaches 40 MB of vram and never more than 1,500 objects in the heaviest of situations.
So a (relatively) simple fix like having and option to make objects in the project bar text-only may correct the problem if I'm thinking about this correctly. An option down the road would be something like a small preview window of an object when you click on it in the list, but something to help larger projects run more stably in C2 would be a huge help.