I have the same issue...
I recently updated my iPad Pro 12.9 to the latest IOS 10.2.1
I then plugged it in to my laptop to transfer from files.
I was then told than in order to access my iPad I would need to update my iTunes software to the latest version 12.5.5
I'm running Windows 10, but like many customers I'm getting an error message (show below) that I am unable to get around no matter what I try.
So I am now stuck with a laptop and an iPad that I cannot use properly. I'm really upset about this. What is Apple doing and what can I do to fix this?
The error message is:
An error occurred during the installation of assembly 'Microsoft.VC80.CRT.type="win32",version="8.0.50727.4053".publicKeyToken="1fc8b 3b9a1e18e3b",processorArchitecture="amd64"". Please refer to Help and Support for more information. HRESULT: 0x80070BC9