Data Source Expression Not Working

Hello, I am trying to use a data source expression but I'm getting an error. Here is my data source expression:



="data source=" & Parameters!ServerName.Value & ";initial catalog=AdventureWorks"



I have created a report parameter called ServerName. However, when I deploy the report and report viewer opens, I get the following error:



An error has occurred during report processing. (rsProcessingAborted) Error during processing of the ConnectString expression of datasource €˜AdventureWorks€™. (rsDataSourceConnectStringProcessingError)



Is there some really obvious step I am missing here? The relevant parts of my rdl are below.



Thanks in advance



<DataSources>

<DataSource Name="AdventureWorks">

<ConnectionProperties>

<ConnectString>="data source=" &amp; Parameters!ServerName.Value &amp; ";initial catalog=AdventureWorks"</ConnectString>

<DataProvider>SQL</DataProvider>

</ConnectionProperties>

<rdataSourceID>(some stuff here)</rdataSourceID>

</DataSource>

</DataSources>

...

<ReportParameters>

...

<ReportParameter Name="ServerName">

<DataType>String</DataType>

<Prompt>ServerName</Prompt>

</ReportParameter>

</ReportParameters>