error "The system cannot find the file specified"

Arduino: 1.8.9 (Windows Store 1.8.21.0) (Windows 10), Board: "Arduino/Genuino Uno"

FindFirstFile C:\Users\AEROSO~1\AppData\Local\Temp\arduino_cache_874837: The system cannot find the file specified.

Error compiling for board Arduino/Genuino Uno.

I'v just started using arduino and im on project 2 in the book. II typed in all the code and tried to upload it just to get that error message.

Try closing all Arduino IDE windows and then try again. That will clear the cache and hopefully fix the error.

pert:
Try closing all Arduino IDE windows and then try again. That will clear the cache and hopefully fix the error.

Yup.

This happens when you have the IDE open for a long time, without compiling anything, and then try to compile a sketch. In the intervening time, windows has cleaned out the temp folder and so the cached core that the IDE expects to find (since it has compiled the core since last restart of the IDE).