Possible reason 1
Your iSlide version cannot be directly updated to the latest version
Please unintall iSlide old version and download the latest version from iSlide official website https://en.islide.cc/download.
Possible reason 2
If you are using Windows 10, it probably due to redidual files. Y
Please unintall iSlide add-in. Then, search for "iSlide" in your computer, delete all the iSlide files. Re-install iSlide in the default location.