Unable To Connect To SQL Database 'MySite-Cache' For Cache Dependency Polling.

 Im getting this error when trying to set up a cache dependency...are there any special permissions etc?
From CS:
SqlCacheDependency dep = new SqlCacheDependency("MySite-Cache", "Products");
Cache.Insert("Products", de.GetAllProductsList(), dep);
From connectionStrings.config:
<add name="SiteDB"         connectionString="Data Source=localhost,[port]SQLEXPRESS;Integrated Security=true;User Instance=true; AttachDBFileName=|DataDirectory|ASPNETDB.MDF" providerName="System.Data.SqlClient" />
Also tried this using my machinename
<add name="SiteDB"         connectionString="Data
Source=<machinename>,[port]SQLEXPRESS;Integrated Security=true;User
Instance=true; AttachDBFileName=|DataDirectory|ASPNETDB.MDF"
providerName="System.Data.SqlClient" />

From web.config:
      <caching>
          <sqlCacheDependency enabled="true" pollTime="10000">
              <databases>
                  <add name="MySite-Cache" connectionStringName="SiteDB" pollTime="2000"/>
              </databases>
          </sqlCacheDependency>
         
      </caching>
 
EDIT:
So making progress I can't seem to get the table registered for cache dependency:
The sample i have says
"aspnet_regsql.exe -E -S .SqlExpress -d aspnetdb -t Customers -et"
and the command line response is
"Enabling the table for SQL cache dependency.
.An error has happened.  Details of the exception:
The table 'Customers' cannot be found in the database."
Where does this "Customers" table come from? There is obviously not an application specific "Customers" table in aspnetdb I'm confused probably more by the example than anything....