Keep Coding

I need to create an item with attachments.
I am using This documentation and following is my xml request:
"<soap:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" "
" xmlns:m=\"http://schemas.microsoft.com/exchange/services/2006/messages\" "
" xmlns:t=\"http://schemas.microsoft.com/exchange/services/2006/types\" "
" xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\">"
"<soap:Header>"
"<t:RequestServerVersion Version=\"Exchange2010\" />"
"</soap:Header>"
"<soap:Body>"
"<m:CreateItem MessageDisposition=\"SaveOnly\">"
"<m:Items>"
"<t:Message>"
"<t:Subject>%#</t:Subject>"
"<t:Body BodyType=\"HTML\">%#</t:Body>"
"<t:ToRecipients>"
"%#"
"</t:ToRecipients>"
"<t:CcRecipients>"
"%#"
"</t:CcRecipients>"
"<t:BccRecipients>"
"%#"
"</t:BccRecipients>"
"<t:Attachments>"
"<t:FileAttachment>"
"<t:Name>FileAttachment.txt</t:Name>"
"<t:IsInline>false</t:IsInline>"
"<t:IsContactPhoto>false</t:IsContactPhoto>"
"<t:Content>VGhpcyBpcyBhIGZpbGUgYXR0YWNobWVudC4=</t:Content>"
"</t:FileAttachment>"
"</t:Attachments>"
"</t:Message>"
"</m:Items>"
"</m:CreateItem>"
"</soap:Body>"
"</soap:Envelope>"
But EWS API returns following error:
<?xml version="1.0" encoding="utf-8"?>
<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
<s:Header>
<h:ServerVersionInfo MajorVersion="15" MinorVersion="1" MajorBuildNumber="817" MinorBuildNumber="11" Version="V2016_10_10" xmlns:h="http://schemas.microsoft.com/exchange/services/2006/types" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" />
</s:Header>
<s:Body>
<m:CreateItemResponse xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types">
<m:ResponseMessages>
<m:CreateItemResponseMessage ResponseClass="Error">
<m:MessageText>Set action is invalid for property.</m:MessageText>
<m:ResponseCode>ErrorInvalidPropertySet</m:ResponseCode>
<m:DescriptiveLinkKey>0</m:DescriptiveLinkKey>
<m:MessageXml>
<t:FieldURI FieldURI="item:Attachments" />
</m:MessageXml>
<m:Items />
</m:CreateItemResponseMessage>
</m:ResponseMessages>
</m:CreateItemResponse>
</s:Body>
</s:Envelope>
Am I doing something something wrong? When I remove attachment section from my XML request then it is working but not with attachment.