Report Server cannot load the extension

Hi,

I am developing a custom delivery extension with user interface for SQL Reporting Services. After some other issues that I was able to solve I finally reach this error here: "Report Server (MSSQLSERVER) cannot load the Custom extension."
Where "Custom" is my extension name.

I don't know where the problem is, this is all information I get. I also tried to deploy the PrinterDelivery sample which is part of the official SDK samples for SQL Reporting Services extensions. The weird thing is that this extension does not produce any event log entries but it is also not displayed in the user interface.

I used this here: http://msdn.microsoft.com/en-us/library/ms153647%28v=sql.110%29.aspx as deployment guide.

What am I doing wrong?