N'I:\\backup\\RestoreAdminData_Forest\\RestoreAdminData_Forest_backup_200905272100.bak'
Are you trying to run this job on the SQL server or through SSMS on your client machine? Have you tried going straight to it with using the UNC path, just "\\\backup..." instead of the drive letter? Do you have other jobs pointing to this network share?
Shawn Melton
Twitter: @wsmelton
Blog: wsmelton.github.com
Github: wsmelton