Incorrect "ERROR: database "xxx" is being accessed by other users"

Hello.

I have a database which I cannot delete (the same for rename):

# psql -d template1
=# drop database xxx;
ERROR: database "xxx" is being accessed by other users

But it is NOT accessed by anybody, because:
1. ps ax|grep post shows that there is NO active connections to database
xxx;
2. I restarter postmaster and immediately try to delete the database - the
same error message
3. I stopped web-server, and now it is GUARANTEED that there is no
connections :-)

What other diagnostics could I do?

P. S.
This database has other stranges, like:
1. VALUUM FULL VERBOSE ANALYZE hands at the middle of this database and
never stops its execution;
2. there are some problems when I create a foreign key to particular table:
it also hangs (postmaster restart does not correct this)
3. database is 2-3 times slow than it could be (if I restore it from the
backup to the new place, it works 2-3 times faster)

Practically I have already dump+restore this database to a new location
(xxx_new) and work with it only, but I want to remove the old (broken?)
database xxx and I cannot...