When attempting to perform a join, the Join option from the Table menu is inactivated ("grayed out").
This may be because the source table already contains a join, the source table is in edit mode, or the join fields are not of the same data type.
Solution or Workaround
The source table contains a join:
Make the source table active and select Remove All Joins from the Table menu.
If the source table is a theme attribute table, convert the theme to a new shapefile to make the current join permanent. Perform the join on the new theme table.
If the table is not linked to a theme in the view, export the source table to a new table to make the current join permanent. Add the new table to the project. Perform the join on the new shapefile.
The source table is in edit mode:
Select the Stop Editing option from the Table menu. Save Edits, if desired. Perform the join.
The join fields are not defined as the same data type:
To determine the data type of a field, look at the values in the join field. If the values are left-justified, it is a string field. If the values are right-justified, it is a number field. Depending on the data type, it may be necessary to: