: Right-click the game in your Library > Properties > Local Files > Verify integrity of game files .

The error is almost always an audio initialization issue. Start by verifying your game files, then move on to updating your audio drivers. In the vast majority of cases, those two steps will resolve the problem and get you back into the lobby.

Call of Duty relies heavily on DirectX for multimedia tasks, including audio. If your DirectX installation is corrupted, the MSS initialization will fail.

There are several potential causes of the "Call of Duty EXE ERR MSS INIT FAILED 150" error, including:

: Incomplete installations or disk errors can damage the executable's ability to call audio libraries.