I want to do a remote backup (from a linux box with w2k3 server) with Backup Exec but I get the following error in Samba logs (I can access the shares directly though) :

svcctl_get_secdesc: key lookup failed! [HKLM\SYSTEM\CurrentControlSet\Services\CMDSERVER\Security] (WERR_BADFILE)
[2006/07/14 10:42:29, 0] lib/debug.c:reopen_logs(597)
Unable to open new log file /var/log/samba/clientname.log: Permission denied
[2006/07/14 10:42:29, 0] lib/debug.c:reopen_logs(597)
Unable to open new log file /var/log/samba/clientname.log: Permission denied
[2006/07/14 10:42:29, 0] services/services_db.c:svcctl_get_secdesc(482)
svcctl_get_secdesc: key lookup failed! [HKLM\SYSTEM\CurrentControlSet\Services\LLT\Security] (WERR_BADFILE)
[2006/07/14 10:42:29, 0] services/services_db.c:svcctl_get_secdesc(482)
svcctl_get_secdesc: key lookup failed! [HKLM\SYSTEM\CurrentControlSet\Services\GAB\Security] (WERR_BADFILE)
[2006/07/14 10:42:29, 0] services/services_db.c:svcctl_get_secdesc(482)
svcctl_get_secdesc: key lookup failed! [HKLM\SYSTEM\CurrentControlSet\Services\HAD\Security] (WERR_BADFILE)
[2006/07/14 10:42:29, 0] services/services_db.c:svcctl_get_secdesc(482)
svcctl_get_secdesc: key lookup failed! [HKLM\SYSTEM\CurrentControlSet\Services\CMDSERVER\Security] (WERR_BADFILE)
[2006/07/14 10:42:29, 0] services/services_db.c:svcctl_get_secdesc(482)
svcctl_get_secdesc: key lookup failed! [HKLM\SYSTEM\CurrentControlSet\Services\BackupExecAgentAccelerator\Security] (WERR_BADFILE)
[2006/07/14 13:51:20, 0] lib/util_sock.c:write_data(557)
write_data: write failure in writing to client 192.168.1.22. Error Connection reset by peer
[2006/07/14 13:51:20, 0] lib/util_sock.c:send_smb(765)
Error writing 4 bytes to client. -1. (Connection reset by peer)

It looks like you are having access errors. Is the backup process being invoked as a cron job and if so is it being done by root? Check the log file it is complaining about and make sure the owner of the backup process has access to it.