Sign into SharePoint 2010 with Facebook using a custom STS

I am using SharePoint2010 on WindowsServer2008 and Integrated with CustomSTS(Facebook).

I can browse the SharePoint site get a Facebook login page, but pressing submit gets the following error back:The action '<EMPTY>' (Request.QueryString['wa']) is unexpected. Expected actions are: 'wsignin1.0' or 'wsignout1.0'.

Any ideas?