Error fix
Saving the load order renames your mod files so Deadlock loads them in the new order. When a file is locked or protected, the rename is rolled back and the app shows this error. The message under it tells you why.
Failed to save mod order
Read the line under "Failed to save mod order" in the notification and match it below.
Quit Deadlock completely, including from the system tray, then save the order again. If the game already closed, wait a few seconds for the process to exit.
Another program has a .vpk open. Close File Explorer windows showing the addons folder, VPK viewers and archive tools. Antivirus scans can hold files briefly, so retry after a few seconds or add the Deadlock folder to its exclusions.
Same cause as above: close the game and any program that has the mod files open, then try again.
Windows is blocking changes to the addons folder. Follow the os error 5 guide to clear read-only flags and permission problems.
Fix os error 5You have more enabled .vpk files than the game can load. Disable mods you don't use, then save the order again.
Saving the order renames the .vpk files in your addons folder so the game loads them in the new order. It fails when Deadlock is running, when another program has a .vpk open, or when Windows denies access to the folder.
No. The app rolls the rename back when a step fails, so your mods stay installed in their previous order. Fix the cause and save again.
No. The game keeps its .vpk files open while it runs, so close Deadlock first. Changes apply the next time you launch modded.
When two mods replace the same file, only one version can load, and the mod order decides which one. Mods that don't overlap work the same in any order.
Deadlock Mod Manager shows which mods conflict and lets you pick the winner by reordering them.