Exchange 2010 installation error - Client Access Role - pls help?

When I tried to install Exchange 2010, everything was ok, but I got this error:

 

Client Access Role
Failed

Error:
The following error was generated when "$error.Clear();
            $aspnet = [System.Runtime.InteropServices.RuntimeEnvironment]::GetRunTimeDirectory() + "aspnet_regiis.exe";
            Start-SetupProcess -name "$aspnet" -args "-ir -enable"
        " was run: "Process execution failed with exit code 1.".

Process execution failed with exit code 1.
Click here for help... http://technet.microsoft.com/en-US/library/ms.exch.err.default(EXCHG.141).aspx?v=14.1.218.11&e=ms.exch.err.Ex88D115&l=0&cl=cp

Elapsed Time: 00:03:43

Mailbox Role
Cancelled

Finalizing Setup
Cancelled

 

Any ideas, suggestions???