Excel RT for tablets, Excel Web App and Excel click to run/Office on demand    
And then there were three

For many years there was just one version of Excel, Excel for the Windows desktop. This is the only version that supports add-ins such as the VT Final Accounts add-in.

A version of Excel is also available for Windows RT, Microsoft's tablet operating system. VT Final Accounts does not run in this version, nor do any other desktop applications.

Finally, there is Excel Online (formerly Excel Web App). This looks somewhat like desktop Excel only it is actually a web page running in a browser. VT Final Accounts does not run in Excel Online.

Excel click to run/Office on demand

Desktop Excel is also available in Click to run and Office on demand versions which are installed virtually (you cannot find Excel.exe in the C:\Program files folder or anywhere else on your hard disk). VT Final Accounts is not compatible with these installations of Excel.

The VT set up program will not proceed if you have Click to run/Office on demand (because it cannot find Excel.exe).

Choose the File>Help command in Excel 2010 or later to see if you have a Click to run installation. In the About Microsoft Excel section, the words Click to run will be shown.

If you have the Click to run version installed, you need to uninstall Microsoft Office and install the normal version.

See also on the Microsoft web site: Click to run: Known issues and Installing a normal version
VT Software>Topics>System requirements>VT Final Accounts>Excel RT, Excel Web App and Excel click to run