You cannot simply download a random ISO. The best fixed PKG for God of War: Ascension has three distinct characteristics:

Once you have the PKG file (and a separate RAP license file if required), follow this guide for a crash-proof install.

God of War: Ascension pushed the PS3 hardware to its absolute limits. It is notorious for its large file size (over 35GB) and heavy use of the console’s RAM.

If you are looking for the "best" performance, the installation method matters.

Solution: This happens if you previously played a different region version.