MKVToolNix v90.0

[Manchita]

Many thanks for your reply Chillgates. I've downloaded what I think is the correct dll...I'm a bit nervous about installing it so I'll wait for a while to see how my computer acts over the next few days. When the error message first appeared it was a surprise because I have used MKVToolNix for years without any problem....and, since the portable version works fine, I was going to ignore the installed version and just use the portable one.
I searched my system with the program "Everything" and it shows there are 6 dxgi.dll's already present:-
C:\Windows\System32            (22/08/2018)
C:Windows\SysWOW64           (22/08/2018)
C:\Windows\winsxs\amd64...   (21/11/2010)
C:\Windows\winsxs\amd64....  (22/08/2018)
C:\Windows\winsxs\x86...        (21/11/2010)
C:\Windows\winsxs\x86....       (22/08/2018)

Thanks again.

EDIT (hours later):- After all the hours I've spent Googling and reading possible causes for this problem and trying different MKVToolNix installers, I finally stumbled onto Reddit and found some other guys who had the same problem...it's related to Windows 7. One of the guys pointed us to https://mkvtoolnix.download/windows/cont...it/67.0.0/ which lists revisions of MKVToolNix 67.0 made during the last 5 days. I downloaded the latest installer and it worked immediately, no error message. I imagine there are other people out there trying to figure out why they are experiencing this "dxgi.dll" error.