Error 1601
The Windows Installer Service could not be accessed.
The Windows Installer service itself is not running or cannot start. Restarting the service, or re-registering it, resolves almost every case.
What it actually means
Every MSI depends on the msiserver service. If it is disabled, damaged or blocked, no package can install regardless of what is wrong with the package.
How to fix it, in order
Ordered by how often each one is the answer, not by how clever it sounds.
- 01Open an elevated terminal and run "net start msiserver". If it reports the service is already running, stop it first with "net stop msiserver".
- 02Check the service is not disabled: press Windows and R, type services.msc, find Windows Installer and set startup to Manual.
- 03Re-register the service: run "msiexec /unregister" then "msiexec /regserver" from an elevated terminal.
- 04Run "sfc /scannow" if it still fails, because a damaged system file can leave the service unable to start.
Common questions
- How do I restart the Windows Installer service?
- In an elevated terminal run "net stop msiserver" then "net start msiserver". If the service is disabled, enable it in services.msc by setting Windows Installer to Manual startup.
Before you retry the installer
If the package came from anywhere other than the publisher, confirm it is the file they actually shipped. Check its SHA-256 against our index, which settles in seconds whether you are debugging an installer or a damaged download.