You have downloaded the CU-8 hotfix from partnersource/customersource and/or are using the LCS Update installer to download and install CU-8 on your AX 2012 R3 RTM.
You have completed the install and been through the software update checklist.
Later you run AX client and click on Help > About, and notice that the Kernel build version has not been upgraded to 6.3.1000.309, but the Application build version has to 6.3.1000.437.
Note: you will also get the similar issues if you instead downloaded the very latest Kernel build 6.3.1000.x and were trying to install this on a system that has Kernel build 6.3.164.x
There is a change in the pre-requirements and the update process is halted due to that.
For example, if you have an older version of the Report Viewer 2012 installed and/or AX Visual Studio Tool (for Visual studio 2010) installed on the system then axupdate will not allow you to update the AOS, Client, Components and Setup Support Files components. Also if you have Retail binary components installed, they will fail to upgrade because the AOS components fail to be updated.
To successfully upgrade the kernel you need to upgrade to the latest Report Viewer 2012 and remove the AX Visual Studio Tools if they are installed. CU-8 or later binary now supports the new Visual Studio 2013 Dev Tools instead.
Further information and answers to some common questions can be found in these posts:
AX 2012 R3 Cumulative Update 8 – FAQ
Announcing Cumulative Update 8 for Microsoft Dynamics AX 2012 R3
Cumulative Update 8 for Microsoft Dynamics AX 2012 R3 now available!
For detailed screenshots of the scenario see attached PDF document