One of the most useful features to fix a variety of Steam game errors is to verify the integrity of the game cache. This process scans your game folder for missing and/or corrupt data, and re-downloads the correct files. To do this:

• Right click Age of Empires 2 in your Steam library.
  
• Click properties from the menu.
  
• The properties window will open up on the General tab. Click the Local Files tab
  
• Click Verify Game Cache

You will get a progress bar as Steam validates the file integrity. If Steam determines any files are corrupt or missing you will see the download bar and a few MB worth of files.

You tried to verify, but are still getting crashes with the same error code 41 message. At this point, your profile has been corrupted and has to be fixed in order to play anything. We can do this by deleting one of the files related to your profile. Doing so will reset hotkey assignments and campaign progress. To repair your profile:

• Go back to the Local Files tab found in properties.
  
• Click Browse Local Files. This brings up the main age 2 install folder.
  
• Double click the profiles folder.
  
• Right click and delete the file called player.nfp.

Your saved games and replays are also susceptible to data corruption. Sometimes it's necessary to flush out that replay and save folder when you catch a nasty case of 41. To make sure your corrupted games don't come back, you will also need to disable steam sync. Here's where to find and delete the saved games and how to shut off sync:

If there is a specific save you really want to save, make a copy of it before deleting. Hopefully that's not the saved game that caused corruption in the first place.

• Go back to properties on age 2.
  
• Click the Updates tab
  
• Uncheck the synchronize checkbox to disable sync for this game only.
  
• Now switch to the Local Files tab.
  
• Click Browse Local Files
  
• Double click and open the savedgames folder
  
• Select all files, right click, and delete files.