I think it's because an event layer is just a temporary (in memory?) layer rather than an actual feature class, so you can't edit it... You need to export the data to a shapefile or a geodatabase first then it should let you edit it.
Hope that helps! Dan
I am simply trying to edit an event layer which has been created from a dbf, but am continuely confronted by the same error window (attached).
This was a simple task in Arcgis 3.2 and 9.1 but for some reason is too much for 10. Can anyone suggest a remedy?
As the help topic mentioned indicated, you need to export the .dbf table to a geodatabase table (file, personal, or SDE) so that the table has an ObjectID field. This same restriction affects QueryLayers and virtually all in memory layer types.
