Fixing the "Can't find filesystemopendialog.dll" error

This is an error that occures when starting the Hammer World Editor, and can be fixed by following the guide below.

Fixing the error

The error is caused by not having a local copy of this file, and can be fixed by doing the following:

• Play Half-Life 2, Half-Life 2: Deathmatch, or Counter-Strike: Source.
• Play the mod you're mapping/modding for (if you're mapping for a mod).
• Check the GameInfo.txt file. Some mods use a certain game to run, and may not be set up properly.
• In GameInfo.txt, when ToolsAppId is set to AppId, you may also experience this error. Try changing ToolsAppId.

SDK Update Fix

Since the 7th November (2007) SDK update, you will encounter this error when using games that use the Episode One engine (HL2, CS:S, EP 1, and all mods). To fix this temporarely, you can switch back to the older engine until a fix is released:

1. In Steam, right-click on Source SDK and choose Properties.
2. Under the General tab, click on the Set launch options... button.
3. Type -engine ep1 in the dialog box, and click OK.
4. Click on Close to return to the regular Steam window.

To switch back to the new engine, follow the same steps as above, but instead type -engine orangebox into the dialog box.