When saving orloading the array, even though you create it with 2 or more dimesnions, only use one dimension when saving or loading it. I believe the save and load array commands only look at the name and the first dimension as a reference to array.
The file extension shouldn't matter.
set window on
cls 0
sync on
sync rate 0
cls 0
randomize timer()
dim pic(100,100)
for x= 1 to 100
for y=1 to 100
pic(x,y)=rgb(rnd(255),rnd(255),rnd(255))
next y
next x
save array "pix_test.bief",pic(100)
undim pic(100,100)
dim openpic(100,100)
load array "pix_test.bief",openpic(100)
for x=1 to 100
for y=1 to 100
ink openpic(x,y),0
dot x,y
next y
next x
sync
Enjoy your day.