I tried a search on error 1722, it returns a lot of hits. Unfortunately that error doesn’t just point to one piece of software.

Adjusting the search string to installation error 1822 brings up many hits but may be better/more related. Some of those mention installing (or trying) a 32bit version on a 64bit system, again this isn’t very definitive.

Changed the search string again to flash player installer error 1722 and that may well have returned more related hits. This one is from the Adobe forum, Error 1722 when installing Adobe Flash Player 10.1 (Active X MSI).

Whilst this is for a different Adobe flash player it may well be related as the AV (McAfee Virus Scan Enterprise) that they had apparently blocked the installation. This would seem a possibility as it seems that AV had setting to protect changes to the browser. That said I haven’t had any issues installing flash player updates on my systems with avast enabled.

Have you made any changed to the avast default settings ?