I'm trying to add an excel file to my data layer (using arc catalog and directly from add Data from file) and having the following error message:
"Could not add the specified data object to the map. An underlying database error occurred. Class not registered."
These links can't be ignored when working with excel since they explain the limitations of using spreadsheets
Understanding how to use Microsoft Excel files in ArcGIS—Help | ArcGIS for Desktop
Formatting a table in Microsoft Excel for use in ArcGIS—Help | ArcGIS for Desktop
Adding a Microsoft Excel table to ArcMap—Help | ArcGIS for Desktop
So see if anything there applies first