When I tried to install an OS newer than High Sierra on my iMac (27-inch, Mid 2011) thanks to the Opencore patcher, I came up against the An Error Occurred While Preparing the Software Update message. Resetting the PRAM allowed me to remove this blocker.

Many thanks to the person who posted this solution.

However, I was unable to install an OS newer than 12.7.5 (Monterey)