autocad installation problem for mac with education license

[massy987]

I'm a student at the first year of architecture. .
I was asked to download autocad .
But I can't. .
I've got a mac.. ?
after I unload the trial version tells me to insert a serial number I don't have..
and despite this when the discharge tells me that it is impossible to install it because I have a version already installed in my pc ( but that is not true)
Please help me.

 

[Tristan]

for the serial number you can use a student license (see here http://ctrl-alt-cad.blogspot.it/2012/05/autodesk-education-community.html ); for the other problem I cannot help you since I do not use mac