Failing update table in db2 with SQLCODE: -668, SQLSTATE: 57016, SQLERRMC: 7;

It follows from the error message, that you somehow submit the entire string Database["DB2"].ExecuteNonQuery("call SYSPROC.ADMIN_CMD ('REORG TABLE DB2ADMIN.XCATENTRYEXT index CATENTRY_ID INPLACE')") as a SQL statement, which obviously is incorrect.

Simply issue these on the shell command line:

db2 connect to <your database name here>
db2 REORG TABLE DB2ADMIN.XCATENTRYEXT

It is possible to do REORG through an SQL statement:

CALL SYSPROC.ADMIN_CMD('REORG TABLE SCHEMA.TABLENAME');