Error during RMAN backup

An Oracle user asks why they are receiving an error when conducting an RMAN backup.

I want to backup an Oracle 9.2 database to a remote network drive using RMAN (with recovery catalog). To do so I mapped a network drive on the database server (which is now drive F:). To check the write permissions I copied some files to F: using the RMAN host command without any errors. Then I tried to do a full backup using the following commands:

run {
    allocate channel disk1 type disk;
    backup full filesperset=100
        (database format 'F:%d_%s.bak' include current controlfile) 
        plus archivelog format 'F:%d_%s.bak' delete all input;
    release channel disk1;
and the following error occured:

RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of backup command at 03/06/2008 11:06:33
ORA-19504: Datei "F:20080306_RMAN_12.bak" kann nicht erzeugt werden
ORA-27040: skgfrcre: Erstellungsfehler. Datei kann nicht erstellt werden
OSD-04002: Datei kann nicht geöffnet werden
O/S-Error: (OS 5) Zugriff verweigert

Do you have any idea what is wrong or missing?
When you run RMAN in this manner, the user who then needs to write permissions to the F: drive is the user that starts the Oracle Service for that SID. This may be a different user that you used to sign on to the server to test with. So make sure the service account has write permissions to this file share.

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