Not an exhaustive list. Not in any order.

* Attempting to upgrade to SQL Server 2016 64-bit upgrade on a 32-bit computer. From what I have seen, this situation is the result of a practice using a workstation as a server and that workstation ran Windows 7 32-bit so SQL Server 2012 32-bit was installed. Later, the practice did an in-place upgrade to Windows 10. The practice never new the computer was 32-bit or forgot.

* Attempting to upgrade to SQL Server 2016 without meeting all prerequisites. SQL Server 2012 MUST be at Service Pack 2 to qualify for an upgrade to SQL 2016. Also, certain Windows Updates must be installed. I've run across several practices who are still running vanilla SQL 2012.

* Too many antivirus programs. Having three or four antivirus programs on the AC server sounds fun. Until your upgrade crashes because they are all fighting to scan the same files.

* AC Server not properly maintained or poor choice made for server. Missing updates, junk programs installed, the list goes on. This often happens when a Windows 10 Home computer was upgraded to Windows 10 Pro or was purchased from a Big Box Store like Best Buy. The computer was never cleaned off and no Windows updates were installed or at least not for a while. In one case, the junk on the machine was preventing installation of updates.

* In-place server upgrade performed to Windows Server 2022. SQL Server 2012, at any service pack level, is not compatible with Windows Server 2022. And now there are issues upgrading to SQL Server 2016.

* SQL Server installed on a domain controller. Good luck with that.

JamesNT

James Summerlin
My personal site: http://www.dataintegrationsolutions.net
james@dataintegrationsolutions.net