Have a look at some other products that may benefit you.
The most likely cause for this is that Maple is installed on this computer.
The main culprit we know about right now is the Windows registry key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppPaths\excel.exe
It contains a value called "Path" which the SigmaPlot installer incorrectly assumes will only contain the Excel path. We know that Maple puts its own path there and that can cause a problem, compounded by the fact that Maple doesn’t uninstall this value.
A temporary workaround is to edit this key so it only contains the Excel path and restore it after doing the SigmaPlot install. If you are comfortable working with regedit (Windows: Run regedit. Click the Windows key bottom-left, write: regedit, and press Enter to start Regedit), the registry editor for Windows, please search for the string ";C:".