In my test database where I have installed my backup of primary database for testing, there I am getting following error whenever the database gets started and when I try to take full export.

ORA-01157 cannot identify/lock data file string - see DBWR trace file
ORA-01110 can open file 201 E:\oracle\ora90\bin\temp01.dbf
ORA-27041 unable to open file
OSD-04002 unable to open file

At the time of starting database the message appeares in alert.log file. After giving the error message the database gets open and every thing is working fine.

On checking the view V$datafile or dba_data_file it is not showing the temp01.dbf.

When I try to add temp01.dbf to temp tablespace it gives error message file already exist.

I have also issued the commend alter system check datafiles. But still got no effects of it.

1. what is wrong ?
2. How to solve it ?
3. Which view I should check after issuing command
alter system check datafiles.