Tentei a cópia oficial mencionada no guia de referência de envio e composição sem sorte (abaixo):

<?xml version="1.0" encoding="UTF-8"?>
<p:ACAUIBusinessHeader xmlns:p="urn:us:gov:treasury:irs:msg:acauibusinessheader"
xmlns:acaBusHeader="urn:us:gov:treasury:irs:msg:acabusinessheader"
xmlns="urn:us:gov:treasury:irs:ext:aca:air:7.0"
xmlns:irs="urn:us:gov:treasury:irs:common"
xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurityutility-1.0.xsd"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:us:gov:treasury:irs:msg:acauibusinessheader IRSACAUserInterfaceHeaderMessage.xsd">
<acaBusHeader:ACABusinessHeader>
<UniqueTransmissionId>token</UniqueTransmissionId>
<irs:Timestamp>2016-12-31T12:00:00</irs:Timestamp>
</acaBusHeader:ACABusinessHeader>
<ACATransmitterManifestReqDtl>
<PaymentYr>2015</PaymentYr>
<PriorYearDataInd>0</PriorYearDataInd>
<irs:EIN>EIN</irs:EIN>
<TransmissionTypeCd>O</TransmissionTypeCd>
<TestFileCd>TestFileCd</TestFileCd>
<OriginalReceiptId>OriginalReceiptId</OriginalReceiptId>
<TransmitterForeignEntityInd>0</TransmitterForeignEntityInd>
<TransmitterNameGrp>
<BusinessNameLine1Txt>BusinessNameLine1Txt</BusinessNameLine1Txt>
<BusinessNameLine2Txt>BusinessNameLine2Txt</BusinessNameLine2Txt>
</TransmitterNameGrp>
<CompanyInformationGrp>
<CompanyNm>CompanyNm</CompanyNm>
<MailingAddressGrp>
<USAddressGrp>
<AddressLine1Txt>AddressLine1Txt</AddressLine1Txt>
<AddressLine2Txt>AddressLine2Txt</AddressLine2Txt>
<irs:CityNm>CityNm</irs:CityNm>
<USStateCd>AL</USStateCd>
<irs:USZIPCd>USZIPCd</irs:USZIPCd>
<irs:USZIPExtensionCd>USZIPExtensionCd</irs:USZIPExtensionCd>
</USAddressGrp>
</MailingAddressGrp>
<ContactNameGrp>
<irs:PersonFirstNm>PersonFirstNm</irs:PersonFirstNm>
<irs:PersonMiddleNm>PersonMiddleNm</irs:PersonMiddleNm>
<irs:PersonLastNm>PersonLastNm</irs:PersonLastNm>
<irs:SuffixNm>SuffixNm</irs:SuffixNm>
</ContactNameGrp>
<ContactPhoneNum>ContactPhoneNum</ContactPhoneNum>
</CompanyInformationGrp>
<VendorInformationGrp>
<VendorCd>VendorCd</VendorCd>
<ContactNameGrp>
<irs:PersonFirstNm>PersonFirstNm</irs:PersonFirstNm>
<irs:PersonMiddleNm>PersonMiddleNm</irs:PersonMiddleNm>
<irs:PersonLastNm>PersonLastNm</irs:PersonLastNm>
<irs:SuffixNm>SuffixNm</irs:SuffixNm>
</ContactNameGrp>
<ContactPhoneNum>ContactPhoneNum</ContactPhoneNum>
</VendorInformationGrp>
<TotalPayeeRecordCnt>0</TotalPayeeRecordCnt>
<TotalPayerRecordCnt>1</TotalPayerRecordCnt>
<SoftwareId>SoftwareId</SoftwareId>
<FormTypeCd>1094/1095B</FormTypeCd>
<irs:BinaryFormatCd>application/xml</irs:BinaryFormatCd>
<irs:ChecksumAugmentationNum>ChecksumAugmentationNum</irs:ChecksumAugmentationNum>
<irs:AttachmentByteSizeNum>0</irs:AttachmentByteSizeNum>
<DocumentSystemFileNm>DocumentSystemFileNm</DocumentSystemFileNm>
</ACATransmitterManifestReqDtl>
</p:ACAUIBusinessHeader>

Obviamente, quando você submete suas próprias informações e as envia no site ISS-UI AATS 2016, apenas diz:

1 error has occurred. See below for more information. If the problem continues, please contact us.

Our system has detected a potential threat in the file you are attempting to transmit and it can not be transmitted. Please check the file and try again. 

Depois de executar o arquivo de amostra nos XSDs, ele mostra que o formato do registro de data e hora está incorreto (ele precisa de um 'Z' no final) e os prefixos em 'irs:PersonFirstNm','irs:PersonLastNm','irs:PersonMiddleNm'não deveria estar lá.

Depois que eu mudei isso, o arquivo passa na validação XSD muito bem, mas o mesmo erro é mostrado:

1 error has occurred. See below for more information. If the problem continues, please contact us.

Our system has detected a potential threat in the file you are attempting to transmit and it can not be transmitted. Please check the file and try again. 

Existe alguém trabalhando atualmente contra o sistema IRS AIR ACA e alguém tem uma cópia do arquivo de manifesto que eles enviaram e que sabem que funciona? Efetuei um ping no serviço de ajuda do IRS para obter mais informações, mas eles levam sete dias úteis para entrar em contato com você.