PowerPivot SharePoint Integration Install Bug

I have recently been doing a lot of work with PowerPivot, and installing it at customers site. I have on two occasions now come across the below error message:

Error: Your SQL Server 2008 R2 installation completed with failures.
            Object reference not set to an instance of an object.

When you view the detail.txt error log, check to see if you see the below towards the bottom of the log:

2010-08-20 14:03:38 AS: Updating IMBI Version of Engine Service instance on local machine failed. Reason:Object reference not set to an instance of an object.
2010-08-20 14:03:38 Slp: Error: Action "Microsoft.SqlServer.Configuration.AnalysisServices.ASSPIInstallFarmAction" threw an exception during execution.
2010-08-20 14:03:38 Slp: Microsoft.SqlServer.Setup.Chainer.Workflow.ActionExecutionException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object.
2010-08-20 14:03:38 Slp:    at Microsoft.SqlServer.Configuration.AnalysisServices.ASSPIConfigExtension.UpdateEngineServiceInstanceIMBIVersionAndUnprovisionedBySetupBit(Version imbiVersion)
2010-08-20 14:03:38 Slp:    at Microsoft.SqlServer.Configuration.AnalysisServices.ASSPIInstallFarmAction.ConfigExistingFarmFirstASServerUseSharedService()

Then you are experiencing a setup bug. Based on the couple of installs where I have experienced the issue, the above error is experienced when you have installed the SQL Server shared files on any other drive except C:. This is even if the case was for other SQL Serve instance instances, as the Shared directory is shared amongst all instances.

Workaround: To rectify this issue, I manually created the directory (shared directory at the following location - C:\Program Files\Microsoft SQL Server\100\SDK\Assemblies) and ensured that the Microsoft.AnalysisServices.SharePoint.Integration.DLL file exists. After this I reran the setup and it worked fine.