SL2b2 cannot invoke void type WCF method?

Hi all~
I saw someone talk about the 404 error of WCF. And give some answers. But no one fit my trouble.
I can get large data, even the list has 10000 rows. When I try to update them. I got the 404 error. But in fact my data has write to SQL server...
I try to change something:
clientaccesspolicy.xml
maxBufferSize
maxRequestLength
maxItemsInObjectGraph
But, nothing!
At the end, I change the type of WCF method to bool, like this:
public void UpdateComponentList(Guid tid, List<Component> source)

{

    using (var db = new LINQDataContext())

    {

        ...

    }       

} 

public bool UpdateComponentList(Guid tid, List<Component> source)
{
    using (var db = new LI ...