You download and begin to install an Exchange Rollup Update only to find after waiting ages for it do the NGen stuff it fails, and on watching it closely you notice it fails on stopping services.
In the event log you are pointed at a website with information on verbose logging for MSI installations.
But you can forget that – the fix is easy! Start and administrative command prompt and run the rollup update from the command line! It will work first time (as long as the update msi file is actually copied to the local machine, it will typically not run from a copy on a network drive.