Disable all mods, restart Steam and check again if the error persists. If you get an error still, it means that the installed mods on your computer are tampering with the client’s performance. If not, you should try running the verification check again. In the ideal case, the files should be replaced or removed. If the manifests don’t match, Steam declares that there is an error and one (or more) files failed to validate and will be reacquired. The manifest on the Steam servers contains the list of all the files which are supposed to be there according to the most recent update. A manifest is a list of files present on your computer. What verifying integrity of a game does is check the manifest of your game with that present at the Steam servers. Like the error states, it found something that it shouldn’t or the mods caused a file to be changed. In many cases, the installed mods for a game may conflict with your Steam client and cause you unexpected errors. There is no specific “one” fix for this solution as the software and hardware configuration of the user may vary. This is a very common problem with a lot of fixes available.

Try to validate the files now and check to see if the issue persists.Players using Steam face a problem where after validating Steam files and the file doesn’t get reacquired at the end of the process.Clicking on “OK” to confirm the clearing of cache. The client will display a warning message that steam will be restarted and you will need to log in again, click on “ OK” when this message is displayed.Clicking on the “Downloads” option from the left pane and selecting the “Clear Download Cache” option. Select “ Downloads” from the left pane and click on the “ Clear Download Cache” option.Clicking on the “Steam” button on the top left corner and selecting “Settings” from the drop-down. Click on “ Steam” on the top left corner and select “ Settings” from the dropdown.Open the Steam client and log in to your account.Therefore, in this step, we will be clearing the game download cache.

Steam stores cache files in order to decrease app loading time and make the experience better for the users however, this cache can get corrupted over time and cause issues with the validation process.

Steam validate gmod file