Fix ERROR_INSTALL_SOURCE_ABSENT 0x64C in Windows 10/11

Cause 1: The original installation media is not available

The number one reason you see 0x0000064C is that the installer is trying to reach a network share, USB drive, or CD that isn't there anymore. This happens when you try to add a feature or repair an installed program, and Windows needs the original source files to do it.

For example, you installed Office 2016 from a network folder that your IT department later deleted. Now you're trying to install a language pack, and boom — error 0x64C.

Fix: Point the installer to the right source path

Windows stores the original install path in the registry. Sometimes it's wrong or the drive letter changed. Here's how to correct it.

1. Press Win + R, type regedit, and hit Enter. Confirm the UAC prompt.
2. Go to this key (or the equivalent for your program, but this is the common one for MSI products):

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Installer\Products

This is a huge list of GUIDs. You need to find the one that matches your program.

3. Look for a SourceList subkey. Expand it, then click on Media.
4. On the right, you'll see a value called LastUsedSource. Double-click it.
5. Change the path to where the install files actually are. If the files are on a DVD in drive D:, type D:\. If they're in a folder called Setup on the D drive, type D:\Setup.
6. Also check the SourceList key itself. Look for a value named PackageName — that's the name of the MSI file you need (like setup.msi). Make sure that file exists in the folder you just set.
7. Close regedit, then try your install again.

After you set the path and close regedit, you should get past the error. If it still fails, the source files might be corrupted, not just missing.

Cause 2: The Windows Installer cache is damaged

Windows stores cached copies of every MSI file in C:\Windows\Installer. If that cache is corrupted, the installer can't find what it needs even if the original media is available.

This often shows up after a system restore or a botched cleanup tool that deleted files from that folder. You'll see 0x64C, and nothing you do with the source path will help.

Fix: Repair the Windows Installer cache

First, check if the cache is actually the problem. Open File Explorer and go to:

C:\Windows\Installer

If you see a lot of empty folders or files with 0 bytes, that's your smoking gun.

You can try a system file check. This is quick and safe:

1. Open Command Prompt as Administrator. Right-click the Start button and choose "Terminal (Admin)" or "Command Prompt (Admin)".
2. Type this and press Enter:

sfc /scannow

Wait for it to finish. It can take 15-20 minutes. If it finds and fixes corrupt files, restart your PC and try the install again.

If SFC doesn't find anything wrong, the cache entries are missing entirely. That's when you need to re-download the installer and run it with the /f option to repair. For example, if you have an MSI file for your product:

msiexec /f "C:\path\to\setup.msi"

This rebuilds the cache from the source. You'll need the actual MSI file for your program. If you don't have it, download it fresh from the vendor's site.

Cause 3: Permissions blocking access to the source

Sometimes the source is right there, but the installer can't read it because of permissions. This is common when the install path is on a network share that requires credentials, or when the folder is on a drive that has restrictive NTFS permissions.

You might be logged in as an admin, but the Windows Installer service runs as a separate service account. If that account can't traverse the folder, you get 0x64C.

Fix: Grant access to the service account

If the source is on a local drive, right-click the folder, go to Properties > Security tab. Click Edit, then Add. Type SYSTEM and click Check Names. Give it Read & Execute permission. Click OK.

If the source is on a network share, you might need to map it to a drive letter with explicit credentials. Go to File Explorer, right-click This PC, choose Map network drive, and enter the path. Check the box "Connect using different credentials" and put in an account that has read access.

Then go back to regedit (as in Cause 1) and set the LastUsedSource to that mapped drive letter (like Z:\).

After you change permissions, give it a minute and try again. This fix works best when the error pops up right after you connect to a VPN or a new user account.

Quick reference table

Start with the registry fix — it's the most common cause and you can do it in two minutes. If that doesn't work, move to the cache repair. And if you're still stuck, the permission fix is the last piece. You'll get this sorted.