Help setting up "Run TestCase"

Hi.

I am trying to set up a "Run TestCase" test step, however, the test step I am trying to call must return a value. I have figured out as much as creating a property for the test case that I am calling.
My problem is how do I return a value from this particular test case's response in the property.

An example to illustrate this:

Create "Run TestCase" TestStep called "teststep1"

"teststep1" is calling "testcase2" which is located in another TestSuite

"testcase2" has a property called "returnvalue"

"returnvalue" is populated with a value from the response of "testcase2" after it has executed

the value of "returnvalue" is available in "teststep1"

At the moment I am using this syntax in "returnvalue" to get the value from the response of testcase2: ${GetMediaSupplierUsers#Response#//GetMediaSupplierUsersResult/a:MediaSupplierUserDto[0]/a:MediaSupplierId[0]/text()}

I hope this makes sense.

Any help would be very much appreciated.

EDIT:

below is the response I am trying to get the value from:

<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
   <s:Body>
      <GetMediaSupplierUsersResponse xmlns="http://contracts.domain.com/instance">
         <GetMediaSupplierUsersResult xmlns:a="http://schemas.domain.com/instance" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
            <a:MediaSupplierUserDto>
               <a:CreatedOn>2013-06-25T14:59:47.25</a:CreatedOn>
               <a:FullName>Full Name</a:FullName>
               <a:IsActive>true</a:IsActive>
               <a:MediaSupplierAttributeCode>Attribute Code</a:MediaSupplierAttributeCode>
               <a:MediaSupplierId>6</a:MediaSupplierId>
               <a:MediaSupplierName>Supplier Name</a:MediaSupplierName>
               <a:MediaSupplierUserId>28</a:MediaSupplierUserId>
               <a:UpdatedOn i:nil="true"/>
            </a:MediaSupplierUserDto>
         </GetMediaSupplierUsersResult>
      </GetMediaSupplierUsersResponse>
   </s:Body>
</s:Envelope>