Hello,

I have a problem; I need to give access to a Windows 2008 Server using the machinename, not a username.

Maybe you think it sounds stupid?
Read this: http://community.spiceworks.com/topic/107157

Example: When you use Windows 2008 server with MS SQL 2008, the SQL2008 process runs under the "Network Service" user account. When configuring SQL backup, it can only reach an UNC path when you give permissions based on MACHINENAME (as you can read in the forum link). There is one other option: Run the MS SQL2008 services (and so the process) under a different user account: i.e.: The 'Administrator' account, although that's another security risk because the Network Service account is a special 'restricted' account.
You can test it when you backup to an Open-E SMB share WITH user-account restriction (this won't work under the Network Service account) and one WITHOUT user account restriction (this works flawless).

Thanks