OCI-19620
string is not of string type
Cause
When opening the file to be placed in a copy or backup set, to be inspected, or used as the target for an incremental restore, its header was not recognized as a valid file header for a file of the indicated type (datafile, archived log, or control file) belonging to the current database.
Action
The indicated file cannot be processed. Ensure that the correct files are being specified for the copy or backup operation.