I installed an offline root CA without issue using this command:

Install-ADcsCertificationAuthority `
-OverwriteExistingKey `
<#In the case of a re-installation#> `
-AllowAdministratorInteraction `
-CACommonName `
"LAB Corporate Root CA" `
-CADistinguishedNameSuffix `
'O=LAB Inc.,C=US' `
-CAType `
StandaloneRootCA `
-CryptoProviderName `
"RSA#Microsoft Software Key Storage Provider" `
-HashAlgorithmName `
SHA256 `
-KeyLength `
2048 `
-ValidityPeriod `
Years `
-ValidityPeriodUnits `
20 `
-DatabaseDirectory `
'E:\CAData\CertDB' `
-LogDirectory `
'E:\CAData\CertLog' `
-Verbose

I installed the root CA's cert and CRl on the policy CA, installed the AD CS binaries, and attempted to run this command to install the policy CA and export a req file:

Install-ADcsCertificationAuthority `
-OverwriteExistingKey `
<#In the case of a re-installation#> `
-AllowAdministratorInteraction `
-CACommonName `
"LAB Corporate Policy Internal CA" `
-CADistinguishedNameSuffix `
'O=LAB Inc.,C=US' `
-CAType `
StandaloneSubordinateCA `
-ParentCA `
rootca `
-OutputCertRequestFile `
'e:\polca-int.req' `
-CryptoProviderName `
"RSA#Microsoft Software Key Storage Provider" `
-HashAlgorithmName `
SHA256 `
-KeyLength `
2048 `
-ValidityPeriod `
Years `
-ValidityPeriodUnits `
10 `
-DatabaseDirectory `
'E:\CAData\CertDB' `
-LogDirectory `
'E:\CAData\CertLog' `
-Verbose

When doing this I receive the following error:

VERBOSE: Calling InitializeDefaults method on the setup object.
Install-ADcsCertificationAuthority :
At line:1 char:1
+ Install-ADcsCertificationAuthority `
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidArgument: (:) [Install-AdcsCertificationA
   uthority], CertificationAuthoritySetupException
    + FullyQualifiedErrorId : ValidateParameters,Microsoft.CertificateServices
   .Deployment.Commands.CA.InstallADCSCertificationAuthority

Is there a parameter I am entering incorrectly or something?