I reckon you should try these out:
- identify the tablespace that file belongs to in the production db.
- put the that tablespace in backup mode on the prod db
- shutdown your standby database
- overwrite the problematic datafile with the corresponding datafile from production database
- put the tablespace above in end backup mode
- startup your standby database and issue the recover command.
Well, there you go. Your standby database should be all fine now.
Well actually it works like this
when you copy the problamatic datafile onto the standby server then it gets synchronised upto the point at which you enable backup for the datafile,and the activities which are done on the prod db after you enable backup for the datafile gets synchronised using the archives generated at the time of enabling and disabling the backup for the problamatic tablespace.