Smart Defrag 2.9.0 r3 un/install errors

I recently got some strange behaviour from Smart Defrag 2.9.0 r3.
Several reinstalls didn't fix it, and eventually I couldn't even uninstall it.

I believe I haven't been using the app for many, many months, but auto-update is on.

First indication, not many days ago, was a Windows (Vista) error popup saying

Smart Defrag Portable cannot be started. You may wish to re-install to fix this issue. (ERROR: App\SmartDefrag\SmartDefrag.exe could not be found)

After uninstall and reinstall it worked again.
Perhaps just the very next time I tried it, it threw the same error.
Now, I did a check, and the exe was there.
Still I did an un/install, and it started again.
After closing the app, not defragging with it, it threw the same error after trying to start it again.
I uninstalled it, but that then threw the error:

Unable to uninstall Smart Defrag Portable

I checked and all the files were gone, though not the folders (I did have the Windows file window open at that location during the uninstall).

I noticed it suggested an in-program update, and it installed a NewUpdate.exe in the App\SmartDefrag(or App\ perhaps).
I never agreed to update.