Using Stored Procedure in NLog on a Database target

I am having a bit of a problem using a stored procedure instead of a SQL INSERT statement when using NLog in a C# web application. The connection string "Logger" is correctly configured in Web.config and works properly when replacing the commandText with a SQL statement. I would appreciate a hint in the right direction. In this example the stored procedure is under the "Logs" schema and it is called "LogError".

<targets>
  <target xsi:type="Database"
      name="dberrorlog"
      connectionStringName="Logger"
      keepConnection="true"   
      commandText="[Logs].[LogError]" >
      <parameter name="@ProgName" layout="MyAppName"/>
      <parameter name="@CompName" layout="${machinename}"/>
      <parameter name="@LogLevel" layout="${level}"/>
      <parameter name="@UserName" layout="${identity}"/>
      <parameter name="@Error" layout="${exception:format=Message}"/>
      <parameter name="@SourceObj" layout="${exception:format=Method}"/>
      <parameter name="@StackTrace" layout="${exception:format=StackTrace}"/>
 </target>
</targets>
<rules>
  <logger name="*" minlevel="Error" writeTo="dberrorlog" />
</rules>