License was not obtained error for Maya

Hello,
I am using Mac OS and trying to get Maya 2013 to run on this Operating System, but when I tried to run it I get the following error message. Please help me with the possible solutions.
Thanks.

License was not Obtained
Tried Maya2013(657E1 2013.0.0.P),error25
License method:
Environment variable MAYA_LICENSE_METHOD=’network’
Product choice:
Environment variable MAYA_LICENSE=’unknown’
LICENSE file override:
Environment variable MAYA_ALT_EN is not set
Abort
