NoCredentialsException while calling web service method

I'm trying to fetch data from Integrity via web services. To get a better picture of the data (), I use SoapUI to call the web services.

However, every method I call fails with NoCredentialsException as answer. I have the needed rights on the project, my request envelope for a call of "getSubprojectList" looks like this one:

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:sour="http://webservice.mks.com/2009/7/Source" xmlns:sch="http://webservice.mks.com/2009/7/Source/schema">

<soapenv:Header/>

<soapenv:Body>

<sour:getSubprojectList>

<!--Optional:-->

<arg0 transactionId="">

<sch:Username>user1</sch:Username>

<sch:Password>xxx</sch:Password>

<!--Optional:-->

<sch:ImpersonatedUser>user1</sch:ImpersonatedUser>

<sch:Project>/repository/test.pj</sch:Project>

</arg0>

</sour:getSubprojectList>

</soapenv:Body>

</soapenv:Envelope>

Here is the complete response soap envelope:

<env:Envelope xmlns:env="http://schemas.xmlsoap.org/soap/envelope/">

<env:Header/>

<env:Body>

<env:Fault>

<faultcode>env:Server</faultcode>

<faultstring>Unable to get subprojects of "/repository/test.pj".</faultstring>

<detail>

<ns1:MKSException class="com.mks.api.response.NoCredentialsException" implication="Unable to get subprojects of &quot;/repository/test.pj&quot;." xmlns:ns1="http://webservice.mks.com/2009/7/Source/fault">Authentication failed for user1 on mks1:9001</ns1:MKSException>

</detail>

</env:Fault>

</env:Body>

</env:Envelope>

Anyone has a hint, what am I missing ?

Thanks in advance, Hendrik