I am finding mybidder increasingly unreliable - and have just found it so again! Is anyone else? Is there anything more reliable?

Please always include the item number in question so I could check.

If you don't want to share it, I could only guess this is related to the recent eBay security issue when they ask everyone to change their passwords.
You must change your password on eBay. Once completed, please don't forget to login to the sniper using your current login information so it will be in sync.