Sort:  

OHhhhhhhh, I think I know what's happening.

Ok, so once you are delegating 0, you can't delegate 0 again. Delegating 0 is undelegating, and if you're delegating 0 again, it's simply not possible to undelegate if you don't delegate already.

So the timeline I think is this:

You delegated XXX amount
You undelegated all to 0
The delegation was coming back, but it still said -XXX in your account (it takes 7 days to return to your funds)
You tried to delegate to 0 again. It said the first error.
You delegated 1
You saw that it's still -XXX because it's coming back. And now that amount has increased by 1.

I think right now you're delegating 1. Delegate 0 again and it will work. And then, you will be delegating 0, but you will still see a -XXX amount in your wallet because it takes time.

Use steemworld.org in the Delegations tab and find how much you're giving. You can remove delegations from there as well.

Thank you. Really appreciate you taking the time to explain it to me :)