Clean/remove previous installs?

As a tester, looking to get an unattended install for everything, Acumatica MSI, a new instance, and our custom plug-ins…  Might be i’m only running into this as i’m iterating on getting what we will be using in the end.  Finding at times the install process is failing with “An instance already exists….”.   Where or how is ac.exe determining a previous install exists…   Having removed:

  • IIS && App Pool
  • SQL Database
  • File and Directory associated for the IIS instances

Most of the time removing all of these have cleaned up or removed the instance,  what else is there?   Really would like to remove the need to run AC.exe and go into App Maintenance and remove the zombie entry...


Best answer by paengesser82 5 September 2023, 21:26

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Userlevel 7
Badge +11

Hi @Dand 

When you install Acumatica configuration wizard, it reflects all previous instances installed (of all versions). One can delete the instance using configuration wizard, which deletes all information about the instance including the virtual directory on IIS except the SQL DB.

One can delete the DB from SQL directly if its obsolete or test instance linked DB. 

Hope this helps,


Userlevel 4
Badge +1

I know this has been awhile, but I stumbled upon this post when looking to do some automation and thought I’d share what I figured out.

Acumatica seems to use the Registry to keep track of instances, so it creates an entry in the Registry which can cause the “an instance with this name already exists” error even when the IIS, SQL, and File Explorer stuff has all been cleaned up.
You can open up regedit and just delete the folder which references the instance that no longer exists.

Path to Acumatica Instances : “Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Acumatica ERP”

This is the article I got some of this information from :

Here is a screenshot incase it adds additional clarity.


Hope this helps,

@paengesser82 , thanks for sharing the solution.


I just would add to restart the computer, after removing the entry from the registry.

It worked for me only after restarting the computer.

Userlevel 7

Thank you for sharing your solution with the community @paengesser82!

Userlevel 7

Hi @Dand - were you ever able to find the solution? Thank you!

Sorry, think your suggestions were to do exactly what has been already done for cleaning up stuff?  I’m seeing instances where:

  • Acumatica does not show up in Windows Add/Remove program.   
  • Deleted all VDIRs in IIS and corresponding app pools.
  • Delete the corresponding folder for the installed instance
  • Remove the database
  • Any folder under “Program Files” or x86

Then run my install for the msiexcec to install the bootstrap setup to get ac.exe, to then run and then fails, a previous instance already exists…  


The question is more about where or how is it getting the information for previous instances. Where exactly is ac.exe once up and running reading the values to show, this is the information i’m really after which seems to be missed…  Is it in a file, registry, some table in Sql’s master db?


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