Hello Jean-Michel,
Thank you for your question about this snipe. It sounds like your authorization for eBay expired or was revoked by eBay. This can happen as a security measure when you change your eBay password, or eBay can reset it if there is a Trust & Safety situation on your account.
You just need to go to Preferences and click the "Log in with eBay" button, and then you are all set.
If you still need assistance, please let me know, and we can take the next step.
bidslammer