Sometime checking the "Remember me" box when signing in clears up things, but I don't think this is the problem.
Other ways to snipe beside "Snipe it now":
1) Use the "My Snipes" tab. You'll see a box titled "Add a new snipe".
2) Also, you'll see "Import Wizard". That will allow you to snipe everything you're watching on "My ebay" page.
Hope this helps.