Can't install Xamarin because Android SDK won't install and I'm going slightly mad please help

I'm running the Xamarin installer and get this :

From the installation log :

Unzipping file '\Temp\Xamarin\downloads\android-ndk-r8d-windows.zip' to directory '\Temp\Xamarin\zips\4c8205ba

Processing ZIP archive internally, external unzip failed

Exception caught while unzipping '\Temp\Xamarin\downloads\android-ndk-r8d-windows.zip'

Ionic.Zip.BadCrcException: CRC error: the file being extracted appears to be corrupted. Expected 0x50F8298C, Actual 0xEB8E465E

I've attached the full installation log.

Can anyone help me resolve this please?

Thanks Gareth