Error creating tables.

Hello
I am new to this list, mostly because I just started using (or trying to) postgreSQL.
I tried to create a table using the example at www.freebsddiary.org/postgresql.html and also at http://www.postgresql.org/users-lounge/docs/7.0/tutorial/query1356.htm . None works.
Tracing down what could be wrong, I came to the conclusion that I can't create any table containing a varchar().
The statement:
create table test4 (name varchar(10)) ;
returns
ERROR: cannot create test4

however, the statement
create table test (id serial, name varchar(10) ) ;
returns:
NOTICE: CREATE TABLE will create implicit sequence 'test_id_seq' for SERIAL column 'test.id'
NOTICE: CREATE TABLE/UNIQUE will create implicit index 'test_id_key' for table 'test'
ERROR: cannot create test_id_seq

But just the statement
create table test3 (id serial) ;
succeedes.

Any ideas?

my system is a K6-2 PC running SuSE Linux 6.3, postgress was installed from the SuSE CDs, not from the sources.
My version of postgresql is 6.5.1

Other error that may be related is that sometimes instead of the error messages I gave (or instead of any return message), psql aborts saying:
pqReadData() -- backend closed the channel unexpectedly.
This probably means the backend terminated abnormally
before or while processing the request.
We have lost the connection to the backend, so further processing is impossible. Terminating.

Any advice is welcome.
Aristide