Problem with wet plaster on lintel above new Sliding door

[abridge]

I have recently had a extension build and had large sliding doors put in leading to the garden. In the last few days i have been getting a damp patch in the plaster board above the sliding doors where the lintel sits. After talking to many people about the issue, i have am still none the wiser as to the actual issue i have. If anyone else has had this issue in the past and if so what was it and how was it fixed. The only things I can think of at the moment is either condensation from the roof space above or a leaking central heating pipe. If anyone has any ideas please let me know.

Andrew B[/img]

 

[JohnD]

I expect it's rain, but if you can post a few pics, we'll see how it's laid out

http://www.diynot.com/forums/viewtopic.php?t=99672