Did you go downstairs and kill the bugs, then go back upstairs and talk to Sven? If so, the silver armour should have been replaced with Larian armour. The Larian armour is invisible on your character, but you can see it in the inventory/equipment panes.
Larian/Silver armour-screenie-spoilerIf you already got Penumbra's dagger and can not find it (the merchant you sold it to would likely still have it);
Lost Items - guide and directory of inventory files 
