Well a regular user shouldn't have the permission's TO save in the Administrator directory. Now are you switching to the admin account when you saved for the second time or are you on the same regular user account? If the latter, then I'm not sure why it work's the second time around. Not sure why it would work at all if your permission's aren't set to allowing you to save in that directory.
My advice is to contact your school's network administrator and alert him of the problem. However he might be curious (as I would) as to why your trying to save in the Administrator directory.