Oracle Database Discussions

Hello All-

I'm working on setting up a Test DB for our Prod System. After much trial and error and help from some experts on here, I can finally get the Test system to recover and open! However, when I attempted to run our night job on it last night, I got an error and was instructed our software consultant to change the 'undo_management' parameter from MANUAL to AUTO in order to successfully run the night job.

So, today I shut the Test DB down with a "shutdown immediate" command (did not recreate the controlfile), then changed the 'undo_managment' parameter in the init file to AUTO and attempted to restart the Test DB using the "startup" command. However, when I do this, I get an error:

SQL> startup
ORACLE instance started.

Total System Global Area 1502242576 bytes
Fixed Size 743184 bytes
Variable Size 452984832 bytes
Database Buffers 1048207360 bytes
Redo Buffers 307200 bytes
Database mounted.
ORA-01092: ORACLE instance terminated. Disconnection forced

SQL>

And in my ".trc" file:

/ubc/oracle/dprtest/dumps/udump/dprtest_ora_1355944.trc
Oracle9i Enterprise Edition Release 9.2.0.6.0 - 64bit Production
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 9.2.0.6.0 - Production
ORACLE_HOME = /ubc/oracle/OraHome1
System name: AIX
Node name: p650
Release: 2
Version: 5
Machine: 0001875A4C00
Instance name: dprtest
Redo thread mounted by this instance: 1
Oracle process number: 12
Unix process pid: 1355944, image: oracle@p650 (TNS V1-V3)

*** SESSION ID:(9.3) 2007-05-03 11:31:40.547
Undo Segment 1 Onlined
Undo Segment 2 Onlined
Undo Segment 3 Onlined
Undo Segment 4 Onlined
Undo Segment 5 Onlined
Undo Segment 6 Onlined
Undo Segment 7 Onlined
Undo Segment 8 Onlined
Undo Segment 9 Onlined
Undo Segment 10 Onlined
ORA-00376: file 20 cannot be read at this time
ORA-01111: name for data file 20 is unknown - rename to correct file
ORA-01110: data file 20: '/ubc/oracle/OraHome1/dbs/MISSING00020'

Then, if I change the parameter value back to MANUAL and log back in and run a regular "startup", Oracle starts and the database mounts and starts without any problems...

What do the
ORA-00376: file 20 cannot be read at this time
ORA-01111: name for data file 20 is unknown - rename to correct file
ORA-01110: data file 20: '/ubc/oracle/OraHome1/dbs/MISSING00020'
errors mean and how do I fix them?

Thanks in advance for your time and help!
-JG