WINDOWS INSTALLER ERROR · ERROR_INSTALL_ALREADY_RUNNING

Error 1618: Another Installation Is Already in Progress

Windows Installer is busy with another installation, update, repair or removal, and it runs only one at a time. Your setup was turned away because of that, not because something is wrong with it.

WHAT WINDOWS SAYS

Another installation is already in progress. Complete that installation before proceeding with this install.

Inside a setup's own window the same condition is message 1500: "Another installation is in progress. You must complete that installation before continuing this one."

Wording from Microsoft's documentation, linked under Sources.

TECHNICAL SUMMARY

Number	1618, 1500
Windows name	ERROR_INSTALL_ALREADY_RUNNING
Where it appears	Exit code of msiexec.exe
In PC Tweaker Uninstaller	Shows the exit code

What causes Error 1618

Another Windows Installer package is in its execution phase. Microsoft says the _MSIExecute mutex is set while that phase runs, and that an attempt to start another installation then returns ERROR_INSTALL_ALREADY_RUNNING (1618).
The same process is still showing the dialogs of another installation: Microsoft lists the user-interface sequence as the second case.
Microsoft points to the installer's event log messages to find out which application is being installed.

How to fix Error 1618, safest step first

Microsoft's own instruction is in the message: complete the other installation first. These steps find it, safest first.

Look for the other installation and let it finish
Check the taskbar and the notification area for a setup window waiting for an answer, and Settings > Windows Update for an update that is installing. Then run the first check below: it lists every msiexec.exe with its command line, which names the package it is working on.
To undo: Nothing to undo: you only looked.
Run your setup again when the list is empty
When the check shows no msiexec.exe apart from the service itself, start your installation or removal again.
To undo: Nothing to undo.
If it never ends, restart the PC
If an installation has been sitting there with no window and no progress, use Start > Power > Restart, Microsoft's first solution for programs that will not install or uninstall. We do not suggest ending msiexec.exe in Task Manager while it is working: an installation stopped halfway can leave that program partly installed.
To undo: Nothing to undo: a restart changes no setting.

Check it yourself, without changing anything

01
List running Windows Installer processes with their command lines (PowerShell)
On Windows 11 build 26300 the Windows Installer service itself runs as msiexec.exe /V; any other line is an installation in progress, and its command line shows the package or product code. Run PowerShell as administrator to see command lines of processes started by other accounts. Nothing is changed.
```
Get-CimInstance Win32_Process -Filter "Name='msiexec.exe'" |
  Format-List ProcessId, CreationDate, CommandLine
```
PowerShell
02
Read what Windows Installer logged (PowerShell)
Microsoft documents event 1033 (installation completed with status) and 1034 (removal completed with status): each names the product, its version and the status number, which is 0 on success. Nothing is changed.
```
Get-WinEvent -FilterHashtable @{ LogName='Application'; ProviderName='MsiInstaller'; Id=1033,1034 } -MaxEvents 10 |
  Format-List TimeCreated, Id, Message
```
PowerShell

What PC Tweaker Uninstaller does with Error 1618

Shows the exit code

PC Tweaker Uninstaller removes a Windows Installer program with the command it shows you first in the Removal Brief, msiexec.exe /x {ProductCode} /qn /norestart, after asking Windows for a restore point when the removal needs administrator rights. It runs one removal at a time, also in a Pro batch, so its own removals never collide with each other. If another program's setup or updater is using Windows Installer at that moment, msiexec.exe returns 1618 and the report shows that exit code. The Uninstaller does not wait and does not retry: run the removal again when the other installation has finished.

PC Tweaker Uninstaller: see the exact command before a removal runs

Common questions

Is message 1500 the same as error 1618?

Yes. 1618 is the exit code msiexec.exe returns, and 1500 is the numbered message a setup shows in its own window: "Another installation is in progress. You must complete that installation before continuing this one." Both mean Windows Installer is busy.

How long do I have to wait?

Until the other installation ends; Windows gives no time. Listing msiexec.exe with its command line shows whether one is still running and which package it belongs to.

Can Windows Installer run two installations at once?

No. Microsoft states that two installations cannot be run in the same process and that a mutex is set while one is executing, so the second gets 1618.

Nothing is installing, so why do I still get 1618?

Something is using Windows Installer without a window. Run the check on this page: an msiexec.exe other than the service's own /V process is the installation that is holding it. If it never ends, restart the PC.