Yes, i know, the problem is that at the moment i do not have any idea what could cause that issue.

I'm using OS globals to get the VRAM base address.... and funny but as i wrote these words, i just remember that there is two way to get that base address, and i'm using the Old way... It is possible that as you're using OS 8, the values a get from the OS globals is false, and points to nowhere, and this causes the app crashing. The next week i will have a "new" LC 475, that supports OS 8, and i will install it next to OS 7...