MS Exchange Server 2013 Error

Error:

The following error was generated when "$error.Clear();

          Install-ExchangeCertificate -WebSiteName "Exchange Back End" -services "IIS, POP, IMAP" -DomainController $RoleDomainController -InstallInTrustedRootCAIfSelfSigned $true

          if ($RoleIsDatacenter -ne $true -And $RoleIsPartnerHosted -ne $true)

          {

            Install-AuthCertificate -DomainController $RoleDomainController

          }

        " was run: "Could not grant Network Service access to the certificate with thumbprint F9629D1AA0890E810D2E96270F63F889731BDD3B because a cryptographic exception was thrown.".