received filename in decoder component

I found several posts which said i could access the name of the received file  with this code snippet

context As IBaseMessageContext = pInMsg.Context

context.Read("ReceivedFileName", "http://schemas.microsoft.com/BizTalk/2003/file-properties").ToString

but it throws an exception (I'm using BTS 2006) if I look if the property is promoted

"ReceivedFileName", http://schemas.microsoft.com/BizTalk/2003/file-properties)

it tells me that it's not promoted. I tried to promote it but this didn't work either. Has anyone a solution for how to get this filename in the decoder component?