Okay, so we're dealing with one machine so yes it does indicate a conflict of some kind and eliminate the installer as being the problem for now.
Can you tell us the make and model of the Vista machine?
The experience I had can be seen in the thread
https://forum.avast.com/index.php?topic=171539.0, where it shows that updating a driver from around 2012 to it's most current (which I think was 2014 from memory) fixed my issue. So without any other suggestions of a solution I'd head in that direction again
You've already indicated that you have the most current Realtek driver; is it an onboard adapter or 3rd-party, and which chipset? There's a possibility that the generic driver is not working as happily with the card as you might expect. Realtek don't make adapters, and vendors sometimes tweak their hardware to work better with their own drivers, so we should look there first before the generic. You could try downgrading this driver to the built-in Windows Realtek generic driver and see what happens too.
Similar idea for the Linksys AE2500. Although the latest driver, it is still from 2011. Windows probably doesn't have a built-in driver for this, but I see on
http://www.linksys.com/us/support-article?articleNum=148503 the Windows 7 and XP driver is the same but Vista is different.
You could try installing the Windows 7 driver, it should work.
In both cases if neither fixes the problem you can always switch back to the original driver.