mixin too low.
This should not happen, is a bug, and should be reported in github if it hasn't been already.
It is supposed to be possible to send pre-existing unmixable outputs with mixin 0. Therefore no mixin would be 'too low'. It can't be guaranteed that you have enough value in the wallet to pay the necessary fees. That's a different issue though, and should not result in the above error. Again, please report the bug.
Report here: https://github.com/monero-project/monero/issues
Click "New issue" and as completely and accurately as possible describe what is going on. Do not include any private information as those issues are public.
OK, thanks will do so.