When we see the error about, 'Could not load file or assembly GTLManagedWindows.dll', it almost always means there is a bitness mismatch between Office and the SAS Add-in.
In other words, the bitness of Office and the bitness of the SAS Add-in have to be the same.
Next steps to take:
1. First, determine the Office bitness.
So open Excel, then select File, Account, click the ?About Excel icon showing the Excel version and bitness.
Make note whether it is 32bit or 64bit.
Then close Excel.
2. Second, uninstall the SAS Add-in.
Then reinstall the SAS Add-in.
3. During reinstall, the install should detect the Office bitness and install the correct SAS Add-in bitness.
However, if a panel labeled 'Select SAS Add-in for Microsoft Office Mode' occurs during reinstall, select the choice for '64-bit Native Mode' if Office is 64bit or select 32bit mode if Office is 32bit.
That should take care of it.
Finally, open Excel and you should have a SAS menu selection.