problem unlocking splinter cell conviction P.E.C challange

[bigjimmyauk]

driving me mad now nearly finished all the challages but having serious problems unlocking complete a level without being seen or re-trying I've just done kobin's mansion 8 times across various difficulties without being seen and it's not unl;ocking i don't even get any white warning let alone and full red warnings.Any splinter cell hero's around here that are having the same problem cause it's really ticking me off now

thanks for any pointers or replies.

I would try the challange on another level but have not yet figured out how to fully stealth complete the other ones without being seen.

 

[bigjimmyauk]

sorted this now kobins mansion appears to be glitched, i ended up doing michigan ave river to get the pec challange complete it wasn't easy tho but did unlock first time. Now to play a level without using a weapon

 

[iamtheoneneo]

you can do this in coop - one person goes ahead kills everyone whilst you wait in the shadows.