Failed to install the Extension Pack D:/Programs/Oracle_VM_VirtualBox_Extension_Pack-4.3.14_RC1-94870.vbox-extpack.
The installer failed with exit code 1: VBoxExtPackHelperApp.exe: error: Not signed with the build certificate.: \Device\HarddiskVolume5\Program Files\Oracle\VirtualBox\VBoxExtPackHelperApp.exe.
Result Code: E_FAIL (0x80004005)
Component: ExtPackManager
Interface: IExtPackManager {3295e6ce-b051-47b2-9514-2c588bfe7554}
I found the same (error message as previous post of Jacob Klein) to be true even after fully uninstalling the 4.3.12 product and the 4.3.12 extension pack. The 4.3.14 RC1 product fails to install its respective extension pack (whether downloading separately first or via the Check Updates function in the GUI).
On Windows 8.1 Update 1 x64...
I upgraded to the new 4.3.14 RC1 94905 build of VirtualBox, and was able to install "Oracle_VM_VirtualBox_Extension_Pack-4.3.14_RC1-94870.vbox-extpack" successfully.
I only use the Remote Desktop functionality, to remote into my VMs, and it appears to work.
On Windows 8.1 (64bit) I was able to successfully install the latest build of VirtualBox (94905) and have it successfully install the extension pack build (94870).