Cheat Engine is a powerful tool used for modifying game memory on the fly, allowing users to cheat or modify game behavior. The "scan" function in Cheat Engine is used to find values in the game's memory that match certain criteria you've specified, such as a health value.
The most common cause of a scan error is an attempt to read a memory page marked as PAGE_NOACCESS or one that has not been committed. When Cheat Engine attempts to read an address within such a region, the OS raises an ACCESS_VIOLATION exception (0xC0000005).