Silent install gives "Another version is already installed...", interactive doesn't.

Hi there,

We're trying to get our continuous integration environment working, and this includes pushing new builds of our SETUP.EXE to servers and having them automatically run to put the latest version of our software down.

We currently do this by running: "SETUP.EXE /S". We have a SETUP.ISS file that we recorded, but it seems really hit or miss whether or not this thing works.

Sometimes it works flawlessly. Sometimes it updates the product version in the control panel, but doesn't update any of the files. Sometimes it fails completely, and I see this in the log:

"Another version of this product is already installed. Installation of this version cannot continue. To configure or remove the existing version of this product, use Add/Remove Programs on the Control Panel."

However, if I actually log into the machine and run the installation by double clicking on it, I get exactly the dialog I expect: "This setup will perform an upgrade of "My Product". Do you want to continue?". I say yes, and everything happens like it should.

What gives? Is there some other command line argument I need to pass to get this thing working right? I've tried /v"REINSTALLMODE=vomus REINSTALL=ALL", but that did the same thing.

Thanks for any help,

Chris