error in step 8 - transport service

hi there,

i need some help here... in the instalation of exchange server 2012 apear this error on mailbox roles: transport service.

how i renew the certificate? that the program ask...

thanks.

Error:
The following error was generated when "$error.Clear(); 
          Install-ExchangeCertificate -services IIS -DomainController $RoleDomainController
          if ($RoleIsDatacenter -ne $true -And $RoleIsPartnerHosted -ne $true)
          {
            Install-AuthCertificate -DomainController $RoleDomainController
          }
        " was run: "System.Security.Cryptography.CryptographicException: The certificate is expired.
   at Microsoft.Exchange.Configuration.Tasks.Task.WriteError(Exception exception, ErrorCategory category, Object target, Boolean reThrow, String helpUrl)
   at Microsoft.Exchange.Configuration.Tasks.Task.WriteError(Exception exception, ErrorCategory category, Object target)
   at Microsoft.Exchange.Management.SystemConfigurationTasks.InstallExchangeCertificate.InternalProcessRecord()
   at Microsoft.Exchange.Configuration.Tasks.Task.<ProcessRecord>b__b()
   at Microsoft.Exchange.Configuration.Tasks.Task.InvokeRetryableFunc(String funcName, Action func, Boolean terminatePipelineIfFailed)".