Same problem here. I rarely visit the Nectar page on eBay (usually check the Nectar app to verify that points have been added), so don't know how long that blue banner has been there on my account, but I note that this thread (which I found by googling the error message) was started near the beginning of this year - and the issue is still unresolved for me and for others.
I'm the sole Nectar account holder (not just the primary one), and have not changed any settings on either my Nectar account or my eBay account to disable the ability to convert Nectar points into eBay vouchers.
At the moment, I'm not too bothered, but sometimes (hasn't happened recently) there is a Nectar/eBay promotion where you can earn bonus Nectar points for converting points into an eBay voucher. I'd like the issue to be resolved before the next promo comes around (if there's ever going to be another one).
I'm still traumatised by my most recent attempts (which failed as usual!) to get a problem resolved by eBay's customer 'service' team, and Nectar's customer service department (which seems to be based in the same part of the world) isn't a great deal better, so I'll keep checking the Nectar section of my eBay account as well as this thread, in the hope that the problem gets fixed without any action necessary on my part.
Another reason I'm reluctant to contact either company about the issue is the accounts on this thread from people who have been batted back and forth between them, with each claiming that the problem lies with the other.
The list of eBay bugs and glitches just seems to keep on growing, doesn't it?
[Edit: Forgot to add that I'm reluctant to try the 'unlink then relink account' method in case that causes additional complications.]
