"ExcelVB" sounds like the name of a Procedure, Module or Workbook.

From the error messages, Excel thinks it is the name of a Workbook.


When creating the code for the Add-In, first create it in a regular workbook similar to the books that will be using the Add-in, Then test the code thoroughly by using Functions in Formulas and running Subs from the Macros Menu. After you are certain that the code works as desired, Drag the Module to an empty Workbook and save that Book as an XLSM