harlequin shadowseer vs multiple overwatch

Had this come up over the weekend: my harlequin seer had Veil of Tears up and I charged a tau suit unit with longstrike within 6", we always ruled that veil of tears works on overwatch, but then this came up:

Longstrike rolls too low on the veil of tears roll
Next, he wishes to overwatch my grots, stating that longstrike can fire multiple overwatches. However veil of tears states that, upon failing, you can not shoot at a different target.

Any thoughts on how this works?

The key part is the end phrase 'this turn' basically, you fail and are unable to this turn (meaning player turn).

As such, I would say no, he could not fire again

I'd say Longstrike is out of luck. Regardless of how many times he can Overwatch, the Veil of Tears ability specifies that if you try to shoot the Harlequins and you're out of range you may not fire this turn.