Please note that this issue is resolved. If you requested a Maya 2012 network license after 25th April and you have a valid Subscription contract, your license will include all the necessary activation codes to run Maya 2012, 2011 and 2010.You will not have to resort to copy/pasting parts of your Maya 2011 license to activate the fluid simulation and mental ray render nodes in Maya 2011.
Your Maya 2012 no longer requires the fluid simulation and mental ray features (including render nodes) to be activated in separate codes. All features of Maya 2012 can be activated from a single activation code. However, a correct license file - issued after the 25th April - will also include PACKAGE and INCREMENT lines explicitely for those features in Maya 2011 and Maya 2010 that require separate activation codes.
If, after you start using your Maya 2012 network license you find that you can no longer render using mental ray or use fluid simulations in previous versions of the application, plesae read the rest of this blog post..
Maya 2012 no longer distinguishes between the Maya component and the sub-features MAYAMFS (for fluidsim) and MAYAMMR (for mental ray rendering) : they're now part of the main Maya license and are not available in the Maya 2012 license file. Previous releases (2010 and 2011) still require these sub-features to be included in the license file as separate components, which is why you need to keep the Maya 2011 license in the license file.
Batch render licenses: You'll also notice that the Maya 2012 license only has a MMR1 feature with five times the number of licenses for each one of your Maya licenses. Therefore the MMR2, MMR3, MMR4 and MMR5 components are no longer needed in the Maya 2012 license.
If you need to render with mental ray or use fluidsim in Maya 2010 or 2011 you need to have the Maya 2011 license in your license file.
For more information, please refer to these Technical Solutions on Autodesk.com
Thanks to Nicolas Holst and Dwayne Poot for their contributions.