Oracle Database Discussions

Dear Guru's,

We have a small, nasty and persistent obscure problem in 9i:

DBVERIFY - Verification starting : FILE = ../oradata2/JAFFA_TSB_1.dbf
Block Checking: DBA = 214030758, Block Type = KTB-managed data block
data header at 0xf6ede264
kdbchk: row locked by non-existent transaction
table=0 slot=107
lockid=1 ktbbhitc=2
Page 121254 failed with check code 6101

Our attempts which do not solve the problem:

1. copy JAFFA_TSB_1.dbf to another partition and perform a alter database rename
2. this block is related to the T_ZIP segment (table) so
a. we made a ddl script of t_zip (including indexes and constraints)
b. made a dump of t_zip
c. drop t_zip and recreate it (assuming when loading it again it will allocate a different block)
d. import back t_zip & run gather statistic on t_zip + indexes of t_zip
e. but when run dbv on data file jaffa_TSB_1 got the same error and again dba_extents shows that this block belong to T_ZIP segment.

We don't think it is a corrupted block because DBV returns the report after this error that there is no corrupted block.

Questions:
1. what is KDBCHK?
2. how can this row be locked?
3. what is the identity of the non-existent transaction?
4. how to remove the lock manually?

Can anyone assist us in this? Oracle support is being contacted, but no solution yet.

Thanks a lot in advance.