no I was just trying to add a join (i.e join an attribute table to another). I got it working, by going through my model really really carefully. It still has a few issues though. I found a lot of the time a join wouldnt work if I just dragged a layer from my map or used the drop down selection, rather than navigating to it using the folder method.
Also the feature class was created from another layer so it was a selection of that layer. Maybe I used the wrong name for it.