If the scanning start and stop addresses are set incorrectly, or if they extend into unreadable system memory, the scanning thread will immediately fault.

[DISABLE] dealloc(newmem)

: Accidentally clicking "First Scan" or "Next Scan" while the "Value" text field is entirely empty.

(e.g., 4 Bytes, Float, String) matches the data you are searching for. If unsure, try setting it to "All". Scan Settings Settings > Scan Settings and ensure that MEM_MAPPED

Cheat Engine saves massive temporary scan data to your hard drive. If these files are locked, corrupted, or deleted mid-scan, Thread 0 throws an input exception.

Even if the game loads, some anti-cheats don't block Cheat Engine entirely. Instead, they inject dummy threads or fake memory regions. When Cheat Engine tries to scan Thread 0, the anti-cheat feeds it garbage data or freezes the thread, resulting in the "please fill something" timeout.

Do you need help finding a (like Float or Double) for the game you are currently modifying?

Windows may be limiting access to the memory range, resulting in a thread error.