This error occurs when using a 3D point shapefile with the field 'Shape' in the IsurfaceOp.Visibility method:
“The table was not found.”
The IsurfaceOp.Visibility method doesn’t support the 'Shape' field of a 3D point shapefile or coverage in ArcGIS 8.1.
Use the Viewshed function in Spatial Analyst. This treats 3D point data as 2D point data; thus, it will allow you to use the 'Shape' field.