Restore msSql database

[AndreinaP]

All users in the server are getting this error when they try to restore an mssql database

Error: dbbackup failed: Unable to restore database 'PruebaRestore'
[Microsoft][ODBC SQL Server Driver][DBNETLIB]SQL Server does not exist or access denied.
[Microsoft][ODBC SQL Server Driver][DBNETLIB]ConnectionOpen (Connect()).

At the server, the event viewer shows the following:
dbbackup.DbBackupException: Unable to restore database 'PruebaRestore' ---> System.Runtime.InteropServices.COMException (0x80040000): [Microsoft][ODBC SQL Server Driver][DBNETLIB]SQL Server does not exist or access denied.
[Microsoft][ODBC SQL Server Driver][DBNETLIB]ConnectionOpen (Connect()).
at SQLDMO.SQLServerClass.Connect(Object ServerName, Object Login, Object Password)
at dbbackup.DbBackupManager.CollectNeededLogins(String database, List`1 neededLogins)
at dbbackup.DbBackupManager.MsRestore(String database, String backupPath, Boolean dropLogins)
at dbbackup.DbBackupManager.Restore(String database, String backupPath, String netPath, String netUser, String netPass, Boolean dropLogins)
--- End of inner exception stack trace ---
at dbbackup.DbBackupManager.Restore(String database, String backupPath, String netPath, String netUser, String netPass, Boolean dropLogins)
at dbbackup.DbBackupManager.Main(String[] args)

I have gaved full control to everyone over the temp's plesk backup directory, but always the same error.

Please, I need to solve this matter.
Thanks in advance.