Getting error for SOAP request "InvalidSecurity : An error occurred when verifying security for the message."

Hi,

I am working on MS Dynamics CRM 2016 integration using SOAP. I was trying to execute WHOAMI request but getting InvalidSecurity error with NTLM authenticaion via SOAP UI.
InvalidSecurity : An error occurred when verifying security for the message.

Please find my soap request snippet here:

POST xxxxxxxx/.../Organization.svc

<env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope" xmlns:wsa10="http://www.w3.org/2005/08/addressing">
<env:Header>

<wsa10:Action env:mustUnderstand="1">schemas.microsoft.com/.../Execute&lt;/wsa10:Action>
</env:Header>
<env:Body>
<Execute xmlns="schemas.microsoft.com/.../Services" xmlns:xsi="www.w3.org/.../XMLSchema-instance">
<request xsi:type="crmtns:WhoAmIRequest" xmlns:crmtns="schemas.microsoft.com/.../Contracts" xmlns:xrmtns="schemas.microsoft.com/.../Contracts">
<xrmtns:Parameters xmlns:scg="schemas.datacontract.org/.../System.Collections.Generic"/>
<xrmtns:RequestId xsi:nil="true"/>
<xrmtns:RequestName>WhoAmI</xrmtns:RequestName>
</request>
</Execute>
</env:Body>
</env:Envelope>
Content-Type: application/soap+xml;charset=utf-8
Accept: application/soap+xml

Am I missing something here?