it looks like you have migrated from v7 to v8 with backup database / restore database operation. Explain tables have been changed from v7 to v8. So you need to drop explain tables manually with drop table commands. Then recreate explain tables with EXPLAIN.DLL script. This script is by default on the following directory: home/db2inst1/sqllib/misc on server site.
This script creates new tables compatible on v8.
Hope this helps,