Thank you for the extra information!
Just as *general* advice, (a) before doing any changes, always create a restore point; (b) don't use KAVREMOVER before trying a standard complete uninstall = do not check *any* check boxes; leave all check boxes blank.
Which version is currently installed? IF it's v21.6, don't do another install of v21.6; v21.7 is rolling out for certain regions, it may be better to wait - which region are you in?
Did you try creating a new Admin acc, as suggested by @Anton Mefodys? IF "yes", what was the result?
In Windows Event viewer, are you able to copy the extended detail of the error shown in the screen print you've posted; paste it to a txt file, & share it here or upload to cloud & post a share link please?
Please let us know?
Also, no, you have to buy a new subscription for Kaspersky Plus, but, read comments by @Danila T., in topic Migrate from KTS 21.3 to Kaspersky Plus 21.5.
The Kaspersky Basic | Standard | Plus - About Subscription is a *starting* point in the Online help library, it's best to log a request with Kaspersky Support, select either Chat or Email, fill in Activation & License issues, Other template; Support will guide you.
(ioo), IF & when Kaspersky do decommission KTS, they will still have to honor existing, valid activation codes; it's not easy getting clear information -> on August 12th, 2022, Kaspersky support advised us: "Soon we will phase out KTS which is why there are no ETA." Frankly we were / are shocked by the "soon"; we hope they've simply been careless with their words. IF you contact Support, please ask them?
Yes, atm the KTS subscription covers installing KIS Premium software on an Android, the Kaspersky Plus subscription will cover installing Kaspersky Standard on an Android.
Please share any Support feedback, with the Community, when it's available?
It seems that v21.6 is now available to download. I am wary of going this route because of the installation error I referred to earlier in this thread. My thoughts are to use the KAV Removal tool and try again. Any thoughts if this should be the next step?
Thanks, reinstalled .NET Framework 4 today as you suggested. But less than 30 mins. ago, another pop up window appeared. I confirm that THIS window was during the automatic updates of the AV. If you'll notice, the parameters are always the same. What changes is the title bar of the window. The previous version 21.3 would sometimes give an error but, at least it offered to analyze the system and send an error report back to Kaspersky. I always sent these reports. This new version gives many more errors with no option to report them.