Possible reason ONE: The add-in doesn't support XP system and is about to support Mac.
Please install Microsoft Office 2010 and later version. Office 2016 / 365 is recommended.
PS: Office 2007 users can only use the offline features.
Possible reason TWO: COM Add-in is disenabled.
Office 2007: Office button at the upper left corner >> PowerPoint Option >> Add-ins >> Management: COM Add-in >> Go to >> open COM Add-in window
Office 2010 / 2013 / 2016: Files >> Options >> Add-ins >> Management: COM Add-in >> Go to >> open COM Add-in window
and check iSlide Tools and confirm.
Possible reason THREE: You didn't re-start the computer after installing .NET Framework 4.5 for the first time.
Re-start the computer
Possible reason FOUR: You didn't close PowerPoint program completely.
Completely close all the PowerPoint processes and open it again. If you are not sure whether you have closed them all, please log off the computer and try again.
Possible reason FIVE: .NET Framework components were destroyed.
Users of Windows 7: Please install .NET 4.5. If you have already installed, please use NetFxRepairTool.exe to repair it and then restart the computer as required.
Users of Windows 8 or later: Directly use NetFxRepairTool.exe to repair it and then restart the computer as required.
Possible reason SIX: The .NET Framework components are not able to be fixed.
Users of Windows 7: Directly uninstall the .NET Framework 4.5 or above (Tools >> Programs and Features >> Uninstall program >> Microsoft .NET Framework 4.5), and then install .NET Framework 4.5 (dotnetfx45_full_x86_x64.exe).
Users of Windows 8 or later: Try to install a higher version of the .NET Framework, such as 4.7.
or download here (Extract Code: 0000)
(iSlide - Tools and Components >> Microsoft.net Framework 4.5)