using Robocopy with a Seagate NAS device

I have set up a shared folder on a NAS device with access permissions given only to "admin" and "administrator".  I log onto a Windows Server as "administrator" and execute a simply copy command via the command prompt to copy a file to the NAS.  This works fine.  I then try from the same command prompt to execute a robocopy command to copy the folder where the file is, to the same NAS box, and I receive an access denied message.  Also, before executing either command, I execute the appropriate net use command to allow access to the NAS shared folder.

The options I use with the robocopy command are /w /mir /t........

I am wondering if robocopy has some limitations I am unaware of.  Any help would be appreciated