When doing an in place upgrade of Windows server 2012 to Windows Server 2012 R2 Preview you hit the following error:
There is not even a compatibility report generated. We have enough free space, no error events are logged except for this one in C:$WINDOWS.~BTSourcesPanther setuperr.logerror log that just mentions Error [0x0807a7] MIG Callback_CreateCompatibilityReport failed[gle=0x00000490]
The trick to deal with this is by not getting install updates online when offered as option in installation wizard.
Otherwise it downloads some bits and then creation of the compatibility report fails. I owe a big thank you to fellow MVP Tomica Kaniski for this tip. I saved me some trouble shooting & time.
My guess is Microsoft will soon have this fixed.
Anyway, now all physical hosts in my home lab are running Windows Server 2012 R2 Preview. We refer to this in our group as having seen the fish 
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Hey! How is it going now? I have a bunch of 2008 R2 machines (both host and virtual) and think how to upgrade them: 2012, 2012 R2 Preview or wait R2 RTM.
Hi,
If it production use you do not want to run an unsupported preview version unless you don’t care about the business. So if it’s production I don’t even know why you’d do this.If it’s a lab it’s all up to you depending on needs. If it’s production you only use supported versions but which one is up to you as well. Look at your needs, evaluate all aspects and decide or hire a consultant to determine the best approach for your business.
Good luck!