Error: Failed to Paste. An Underlying Database Error Occurred.
"Failed to Paste <Table_Name>
An underlying database error occurred.
The changes you requested to the table were not successful because they would create duplicate values in the index, primary key, or relationship. Change the data in the field or fields that contain duplicate data, remove the index, or redefine the index to permit duplicate entries and try again."
Indexes on text fields are case-insensitive in personal geodatabases that are built on the Jet Database Engine. Text field values are case-sensitive in other DBMSs supported by the geodatabase, such as Oracle. Therefore, a table in Oracle may have a unique index on a text field that contains the values 'A' and 'a'.
When trying to copy/paste this table to a personal peodatabase the error above is received because the Jet Engine allows case-insensitive indexes on text fields and the values in the field are not considered unique by the database.
In this situation the table is created within the geodatabase, but the index is not created.
Solution or Workaround
Prior to the copy/paste, create a non-unique index on the field.
Drop the index prior to the copy/paste and recreate it in the source and target geodatatabases after the paste.