Sling load not working

[TOViper]

Guys, in MP last week I had serious troubles with sling loading a 23mm Howitzer on HACA DYCA server.
I select # > F6 > 23 mm gun > I see red smoke on the package > I see the rope coming; my buddy in the OH-58 didn' see the rope > I try to tension it > in 400 ft above ground still no tension > I release.
When trying to select another cargo with # > F6, I see the menu option "Cancel hooking cargo"; it never disappeared, even after selecting it several times, so I was not able to select another cargo then.

I tried two times with 2 UH-1s within the same mission, but to no luck.
Is this related that the carg used in the mission is NOT a specific "UH-1 Cargo"?