If a non-numeric value is entered as a buffer distance in the 'define multiple buffer polygons' panel of the Buffer Wizard, ArcToolbox returns the following error message:
Note: This article applies to retired ArcGIS versions 8.x. Later versions of ArcGIS may contain different functionality, as well as different names and locations for menus, commands and geoprocessing tools.
The input buffer distance is not being validated. The tool requires a numeric value as a buffer distance but does not enforce it on the form leading to the type mismatch error.
Make sure only numeric values are entered as buffer distance values on the 'define multiple buffer polygons' panel.