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
I've you've moved the system TEMP folders, try moving them back to the original C:\Windows\TEMP

I've seen that cause the problem.