Possible reason ONE:
iSlide feature panel shows as follows:
Microsoft PowerPoint 2007 doesn't allow you to log in and use the online features. To enjoy full features of iSlide, please upgrade your Office version. Office 2016 or Office 365 is recommended.
Possible reason TWO: Local file configuration disordered
Enter %LOCALAPPDATA%\Microsoft_Corporation in the address bar of Explorer, and then you can see several folders, please delete them all.