No password supplied error when running a batch script as a programmed task

I wonder if this question belongs here. Please let me know in order to look
for another place to ask.

I have PostgreSQL installed on Windows Server 2008 R2 and wrote a batch
script to get a backup of a database. Such a script must run automatically
so I created a task in the Task Scheduler which runs under the
Administrator account. This task fails running the batch script and
provides the following message:

fe_sendauth: no password supplied

However, if I run the script directly double clicking of it, the batch
executes successfully. The pgpass.conf file is also correct, otherwise, the
batch script would not run manually.

I will very much appreciate your feedback.

The batch has the following instructions:

echo off
d:
cd "D:\Program Files (x86)\PostgreSQL\9.3\bin"

SET mes=%date:~3,2%
SET dia=%date:~0,2%
SET anio=%date:~6,4%

IF %TIME:~0,2% LSS 10 (SET hra=0%TIME:~1,1%) ELSE (SET hra=%TIME:~0,2%)
IF %TIME:~3,2% LSS 10 (SET min=0%TIME:~4,1%) ELSE (SET min=%TIME:~3,2%)

echo on
time /t
rem echo off
pg_dump -E win1252 -f
d:/respaldos/edocuments/edoc_%anio%%mes%%dia%_%hra%%min%.backup -F p -n
edocuments -h localhost -U postgres -w edocuments
pg_dump -E win1252 -f
z:/respaldos/edocumentsdb/edoc_%anio%%mes%%dia%_%hra%%min%.backup -F p -n
edocuments -h localhost -U postgres -w edocuments
echo on
time /t
rem echo off
pause