During the DCAU cartoon series Batman Beyond, we hear mention of Dick Grayson, the ex-Nightwing and how he and Bruce have not been on speaking terms for many years.
In the 2011 comic book continuation (Batman Beyond Vol 3) by Adam Beechen, Nightwing shares that:
The Joker had kidnapped Alfred and when Dick and Bruce went to the rescue, Dick got riddled with bullets, due to Batman being unused to working with a partner for "years". The incident left him Nick Furyesque in the eye but also left a bullet stuck near his spine.
The situation leading to the incident is portrayed in the below flashback.
Dick: He'd been alone so long--since what happened to Silver-- and he hadn't worked with a partner in years.
Joker being the perp here, means this is clearly before the flashback parts of Return of the Joker, so by all accounts Batman should be working with Batgirl and Robin II (Tim) at least somewhat regularly during this time. And Silver is name-dropped significantly but the only Silver that seems to crop up in a DCAU context is Silver Banshee - a minor JLU villain with no connections to Batman.
So who/what is Silver and what is the incident being referred to here? Why is Batman 'alone' during this time period?