I press Line 5 on a 7961 and CFwdALL and get That Key is Not Active here. Line 5 is not part of a Line Group or Hunt Pilot and is not a Shared Line.
Line 5 has a good Calling Search Space, maybe there is a enterprise parameter that was added in 4.x?
This used to work in 3.x (forward on per line). CFwdALL works for line 1 but not lines 2-6 on the 7961?.