I want to migrate the instance "db2sp1" and issue:

# ./db2imigr -u db2sp1 db2sp1

db2ckmig was successful. Database(s) can be migrated.

DBI1222W The system database directory is corrupted and cannot
be migrated.

Explanation: Either the primary and backup system database
directory files are not the same or system database directory is

User Response: Remove system database directry and re-catalog
all database entry.

I am quite sure there is nothing wrong with database directory as I
droped all the databases already!

Who can tell me what is wrong and how to migrate it?

Due to some reasons, I can not install UDB 7.2 directly, must upgrade!
But I do not care about the database!

Thanks in advance