ERROR: CREATE DATABASE

Hallo
I am so sorry to bother you with this (I guess) elemental question, but
after two days of changing permissions and paths I do not know what to
try next.

I have downloaded and compiled and installed all the software in the
distribution on a Sun Ultra 10 running Solaris 2.6. This was easy
following your excellent documentation (really good, indeed).

I have used exactly the same tree directory that you present in the
installation guide. The only difference in this point was that the
untared source of the distribution was in my directory
(/home/user/shareware)

After the installation (where I could not appreciate any abnormal
behaviour or warning message) I have started the postmaster as the
postgres user.

After this I have used the command
> createdb testdb
and the answer is
ERROR:  CREATE DATABASE: Could not initialize database directory. Delete
failed as well
createdb: database creation failed

When I use the psql program with
> psql template1
it works fine, and when I use CREATE DATABASE testdb, I get no error
messages. If I quit after that and run
> psql testdb
The message is
psql: FATAL 1:  Database "testdb" does not exist in the system catalog.

I know you must have lots of better things to do than answering to this
nubbie question, but I have run out of ideas, so I would appreciate any
help. Thanks a lot in advance.

Javier Quiles