another stupid question: Database is being accessed by other users

sorry for asking again, because i could solve this problem on my own if i had 
enough time to check things.

i collect all my sql command and do
#!/bin/sh
dropdb kontaktdaten
createdb kontaktdaten
cat sql_commands | psql kontaktdaten

and often i get

ERROR:  DROP DATABASE: Database "kontaktdaten" is being accessed by other 
users    

if i do a ' ps ax | grep post ' i see some processes which are idle
2572 pts/6 S 0:00 /usr/bin/postgres localhost wwwrun kontaktdaten idle 

i always call pg_Close in my php scripts. Why are there still some processes 
and how can i achieve to drop the database??

thanks in advance for any help or suggestions

janning