Are you using a of the game, or are you trying to get an older physical disc version to work on a modern PC?
Because this file is often modified in "repack" or "cracked" versions of the game, many antivirus programs (including Windows Defender) flag it as a "False Positive" and delete or block it.
If you own the game on a platform like Steam or the EA App, the launcher can automatically detect and replace missing files.
Here is the most important section of this article.
If you're experiencing any of the following symptoms, it's likely that the aeyrcdll file is missing or corrupted:
While the "aeyrcdll.dll missing" error in Crysis 3 is frustrating, downloading the file from a third-party site is a gamble with your PC's security. By using the "Verify Integrity" feature on Steam or the "Repair" function on the EA App, you can safely replace the missing
Missing DLL errors in are often caused by antivirus software incorrectly flagging and quarantining game-essential files during installation.