One of the reasons why this error would be thrown if you are using an internal Microsoft Enterprise CA is if the issuing Root CA’s certificate has expired. Command execution failed: Error Parsing Request A required certificate is not within its validity period when verifying against the current system clock or the timestamp in the signed file. WARNING: Detailed results can be found at 'C:\Users\ccs.contosoCORP\AppData\Local\Temp\Request-CSCertificate-.html'.
> Request CertificateRequest-CSCertificate -New -Type Default,WebServicesInternal -CA '\Contoso CA' -Country 'BM' -State 'Hamilton' -City 'Hamilton' -FriendlyName 'Skype for Business Server 2015 Default certificate ' -KeySize 2048 -PrivateKeyExportable $False -Organization 'Contoso' -OU 'IT' -AllSipDomain -Verbose -Report 'C:\Users\administrator\AppData\Local\Temp\Request-CSCertificate-.html'Creating new log file 'C:\Users\ccs.contosoCORP\AppData\Local\Temp\Request-CSCertificate-.xml'.Create a certificate request based on Skype for Business Server configuration for this computer.Creating new log file 'C:\Users\ccs.contosoCORP\AppData\Local\Temp\Request-CSCertificate-.html'. You’re attempting to renew the Skype for Business Server 2015 front-end server with an internal Microsoft Enterprise Certificate Authority but receive the following error:
