if you get one Modern Warfare 2 connection lost due to user error, there is a quick and easy solution. All you have to do is just stop tapping the cancel button when the game connects to the server.
How to fix connection interrupted by user error in Modern Warfare 2
As mentioned above, if you press the button to end the connection, you will get the error Connection Interrupted by User in Modern Warfare 2. It seems strange that this is showing a strangely worded error which can confuse things.
Unfortunately, it’s very easy to accidentally cancel the server connection dialog by pressing the confirm button too many times. There is no confirmation dialog to check if you really want to end the connection. It just stops immediately and displays the error.
Fortunately, if you accidentally cancel, you can immediately start connecting again by pressing the confirmation button again. Then the game should work as expected.
Hopefully the Infinity Ward developers make the whole process a little less tricky, or at least make the error message more helpful. As it stands, the whole thing seems to be a lot worse than just terminating the server connection.
https://www.gamerevolution.com/guides/714972-modern-warfare-2-connection-interrupted-by-user-error-fix Modern Warfare 2: Fixed connection lost due to user error