If we will not give the CLOSE_GROUP function module this is
happend.

Suppose if you want to another session how to open? without
closing this function module you cannot open the another
session. so that purpose we should close this function module

BDC_CLOSE_GROUP

The session created in SM 35 will be in having creating 
status and we cannot prosses it. So we much call this 
function moduel then only the session which will be created 
can be processed

BDC_CLOSE_GROUP needs no parameters. It automatically closes
the session that is currently open in your program.

You must close a session before you can open another session
from the same program.

You cannot re-open a session once it has been closed. A new
call to BDC_OPEN_GROUP with the same session name creates a
new session with the same name.