Cannot open backup device 'F:\foldername'. Operating system error 5(Access is denied.).

Question

SQL 2005 Enterprise
Even if I logon as Administrator and try to backup any of my databases to local partitions, I get this error below. I have been operating fine up until this point and doing backups all the time.  As far as I know, and after checking, no permissions have changed and of course Administrator has ntfs permissions to my local C and other partitions on this server:
TITLE: Microsoft SQL Server Management Studio
Backup failed for Server 'servername'.  (Microsoft.SqlServer.Smo)
For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&ProdVer=9.00.1399.00&EvtSrc=Microsoft.SqlServer.Management.Smo.ExceptionTemplates.FailedOperationExceptionText&EvtID=Backup+Server&LinkId=20476
ADDITIONAL INFORMATION:
System.Data.SqlClient.SqlError: Cannot open backup device 'F:\foldername'. Operating system error 5(Access is denied.). (Microsoft.SqlServer.Smo)
For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&ProdVer=9.00.1399.00&LinkId=20476
BUTTONS:
OK
In the Event log for Windows Server 2003 I see this:
Event Type: Error
Event Source: DCOM
Event Category: None
Event ID: 10016
Date:  3/6/2006
Time:  3:35:06 PM
User:  NT AUTHORITY\NETWORK SERVICE
Computer: servername
Description:
The application-specific permission settings do not grant Local Activation permission for the COM Server application with CLSID
{BA126AD1-2166-11D1-B1D0-00805FC1270E}
 to the user NT AUTHORITY\NETWORK SERVICE SID (S-1-5-20).  This security permission can be modified using the Component Services administrative tool.
For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.

Answer 1

SQL Service account is DOMAIN\SQLAdmin
Have given the SQLAdmin AD account access to the Backup shares on the file servers (2 file servers, FILE1, FILE2)
and I still get the error
Operating system error 5(Access is denied.).
RESTORE FILELISTONLY
FROM DISK = N'\\SERVER\APPS\backups\UA\DB\DB.BAK'
I trid to attach it as device, which runs
sp_addumpdevice 'disk', 'Network_Share', '\\SERVER\backup\APPS\UA\DB\DB.BAK'
BUT when restoring, same error occurred (Access denied)
Only case I can backup/restore to/from network shares, is from the machines where SQL Server runs (SQL1, SQL2)
e.g. I copy the BAK file from FILE1 to SQL2, share the folder (add SQLAdmin account with access), then restore on SQL1 with file from SQL2 Share
RESTORE FILELISTONLY
FROM DISK = N'\\SQL2\backups\UA\DB\DB.BAK'