Question: I was trying to install Exchange 2010 prerequisites, when I encountered some error. All look like the same. Like this one:  

`Error: Installation of [Windows Process Activation Service] Configuration APIs failed. the server needs to be restarted to undo the changes.`  

My server is running Windows Server 2008 R2 Standard Edition.  

UPDATE: I tried installing the prerequisites one by one using PowerShell.
Now I have errors on RPC over Http proxy: 

> 
> Installation of [Web Server (IIS)]
>  Tracing Failed, Attempt to install
>  tracing failed with error code
>  0x80070643. Fatal error during
>  installation.
> 
> 
> 

Searching about the error code doesn't tell me much more than something went wrong when trying to update windows.   

Installing Http Tracing alone also doesn't make any difference.

Answer: 
Try turning off UAC, rebooting & installing the pre-req's
This error also occurs when the server you are adding the feature to is using an IIS Shared Configuration setup. 

In this case it is sufficient to remove the Shared Configuration, install the feature and then re-enable the Shared Configuration.