Tough deleting sprites will result warning message, I found another way AGS crashes.
I tried to logically do right, but that resulted a crash.
This is what I did:
I drew some of my sprites over and made duplicate ones. When replacing the old ones in a view with newer ones, I removed all the old sprites from a loop.
Then I deleted them from Sprite Manager, thinking that as they're not assigned to a view anymore, It's safe.
Well, it wasn't.
When trying to put new sprites into same loop, AGS usually goes to a folder in Sprite Manager where old, just deleted one was and tries to select the old sprite. And that caused the error, because old sprite was no more there. I got an error message and pressing ok caused same error message to appear again and again, which left me no other option than press Ctrl-Alt-Del and force AGS to close.
Once again, long story about a little bug.
AGS pre-selects the last used sprite in the view editor when creating new frames, right? And if the sprite number no longer exists, it would be logical to jump to the blue cup sprite, number 0. Right? This is what I've seen...
I think I've heard of something like this happening, and a work around was just import some temp sprites (so the sprite number is filled again that it was looking for) then you can go and find the sprite you want.
I could be thinking of something else though, but it seems logical.
Ah I see yeah, it remembers the last sprite you selected in the sprite manager, and if you then delete that sprite it crashes.
I'll fix it up for the next version.