trouble with table creation

Hi, fellows!

I'm getting crazy with a stupid question. I have just created a Database
using pgadmin.exe, then I've created a table named "tabCliente" and, of
course, wanted to populate it. Everything was working fine since I tried to
use pgadmin's sql tool. An idiot sentence like "insert into tabCliente
(iCodCliente, nomCliente) values (NextVal('sqCliente'), 'Nome do Cliente')
resulted in an error message like this:

"Error: -2147467259
Error while executing the query (non-fatal);
ERROR: Relation 'tabcliente' does not exist

function: frmSQL, cmdExecute_Click"

Please! Anyone know what have I missed? Is that a problem with pgadmin?
Help me, please!

The user has total privileges over the database.

Thanks in advance for any advice.

Regards,

Paulo