i was importing windows 8.1 Virtual Machines in Windows server 2008 r2 Hyper-V environment so i have faced many issues in importing the VMs, so i experienced that you can not directly import windows 8.1 or windows server 2012 Virtual Machine into windows server 2008 r2. you have to convert the VHDX into VHD then you will be able to import in windows server2008 r2, i was wondering to write a blog post on this topic. Please follow these steps to convert it into VHD.
Open your Hyper Server
Right click on the virtual machine which you want to export and click on setting option
Click on hard drive option on your left and then click on edit button.
once located and selected click on next
you will new be prompt with 3 options
now select what version you want to convert in my case i wan to export in VHD. click next
when you initially created the virtual machine if you accidentally dynamic instead of fixed here id one way to change that. if you want to keep it the same in this case dynamically available just click next
Select the path where you want to save this VHD
now click on finish to start the process
now wait for a while it will save your VHD in your given path. after complete this process you can import this VHD in Windows server 2008 R2.
Thanks and Regards