Problems with pg_dumpall

Hi;
I'm using postgres7.3.4 and I have tried to use pg_dumpall to copya a
database from one computer to another. I remember I used it once with no
problem, but now I've found a lot of error.

I've run the restore as the "postgres" superuser, and it seem that when a
table exists previously, or a language or another element, this creates an
error.
Please. How could I resolve this? Perhaps should I DROP all tables previously
to the restoration?

Thanks, and best regards,

Javier