Did you change you eBay password between the times you looked? That would do it. From the FAQ's:
I changed my eBay password and now I can't find any of my scheduled snipes on Gixen. What happened?
The snipes were effectively canceled when you changed your eBay password. This is by design. Note that unlike other sniping services, Gixen does not store eBay passwords longer than necessary to execute snipes: it only stores them for 48 hours past the latest scheduled snipe. Every snipe is saved as (item_id, username, password, bid) in the database; thus, changing your password cuts the database links to your scheduled snipes, effectively canceling them.