Berlingo driver side sliding door won't unlock

[Wullie 64]

Hi there. I have a 07 Berlingo Desire. the driver side sliding door won't open. 
You can see the internal panel switch go up and down into position but it will not unlock either from the inside or outside mechanism. Any ideas what could cause this?
Cheers.

[ffrenchie]

Probably linkage disconnected inside the door.