Update: Using the MR2 image with the following agents, I am able to push and pull images using a clean install of 5.7.2 on a Windows 2012 R2 server; Boot Agent 3.4.4 Agent 12.1.4.2 
I am unable to push an image from WDM to my 5020 device, I receive the following error: 1:Merlin-Process-FAILURE [Wed Sep 28 11:39:37 2016][ERROR: Invalid image package.  (error code : 101).][ERROR STAGE:  Package validation.][REASON: The size of the mbr.img component in package script does not match the actual size of the mbr.img component.][SOLUTION: Re-register the valid image package.] (Package GOGO_0A0F_32GB)  I am also unable to pull an image from my 5020 device, I receive the following error:  1:Merlin-Process-FAILURE [Wed Sep 28 11:11:18 2016][ERROR: Error while uploading MBR file. Http Error code : .][ERROR STAGE: MBR validation.][REASON:  Flash is corrupted or improper repository/network configuration.][SOLUTION:  Disable anonymous authentication if enabled on software repository under MyWDM virtual directory or check the device flash.]   WDM 5.5.1 (clean upgrade from 5.0 to 5.5 to 5.5.1) Server OS Windows Server 2008 R2 (dedicated) Device: 5020 Windows 10 IoT Pro Boot Agent 3.3.3 for WIE10 HAgent version: 6.3.5.9  
Unable to Push or Pull from 5020 or 7020