rman cannot write to CIFS share

Hi,

I have a win 7 server with oracle 11.2.0.4 SE (old system).

We have a synology to use as a backup drive (there is no domain, just a workgroup).

As ORA_DBA member and as Administrator, I can write to that folder:

echo z >\\172.17.3.30\prdb\bu\test.tst

works, file is created.

backup script is

run
{
allocate channel ch1 device type disk;
set limit channel ch1 kbytes 40097152;
sql 'ALTER SYSTEM ARCHIVE LOG CURRENT';
delete noprompt obsolete;
BACKUP AS COPY CURRENT CONTROLFILE FORMAT '\\172.17.3.30\prdb\bu\controlfile%U.ctl';
backup SPFILE format ''\\172.17.3.30\prdb\bu\sp_%n%T_%U%p';
backup database format ''\\172.17.3.30\prdb\bu\db_%n%T_%U%p';