1601
App Installer (MSI)
The Windows Installer Service Could Not Be Accessed
Applies to: Windows 7, Windows 10, Windows 11
What it means
The Windows Installer service itself isn't running or responding.
Also seen as: error 1601
Quick fix steps
- Open Services (services.msc), find "Windows Installer," and make sure it's set to Manual and running.
- Restart the PC and retry.
- Run "sfc /scannow" if the problem persists, in case a related system file is corrupted.
For the full step-by-step walkthrough, see An App Won't Open.
Frequently Asked Questions
Does this mean Windows Installer is broken?
It suggests the Windows Installer service isn't running or responding properly, which is usually fixable by restarting the service rather than indicating permanent damage.
Is Windows Installer the same as the Microsoft Store?
No — Windows Installer (msiexec) is the older, traditional technology many desktop programs use for installation, separate from the Microsoft Store's app installation system.
Other error codes
1603 — Fatal Error During Installation
A generic installer failure code — the real cause is almost always in the detailed install log, but common triggers are permissions, a locked file, or insufficient disk space.
1618 — Another Installation Is Already in Progress
Windows Installer thinks another install is running, even if nothing visibly is — usually a stuck installer process from a previous attempt.
1601 — The Windows Installer Service Could Not Be Accessed
The Windows Installer service itself isn't running or responding.
1602 — User Cancelled Installation
The installer detected what it interpreted as a cancel action, sometimes triggered incorrectly by antivirus software or a UAC prompt timeout.