Hi Peter and thanks for that..
all contacts are in good order and depress and return nicely when pushed.. i have cleaned themn sufficiantly i beleive (lens was in as new condition when bought) and camera was purchased in march!
i have been around with a precision screwdriver and tightenened things up although nothing was loose as such.. just a small amount of turning available on a couple of screws.
after depressing the contacts on both the camera and the lens the problem seems to of gone away so maybe something wasnt sitting right somewhere..
it did take a bit of a knock but nothing too bad.. the bag was sat under a table when i got cramp in the back of my leg and i caught the bag just as i kicked and stood up!
i dont think i hit it hard tho .. just glanced..
we do have a sigma service centre close by so i can drop it into them if the problem surfaces.. i was on about getting it serviced anyway.
Thanks
Steve