Make sure that AMBERHOME points to /usr/local/amber16 :

#
# cat leap.script 
source leaprc.protein.fb15
source leaprc.water.fb3
fsd1 = loadPdb aligned.pdb
check fsd1
solvateBox fsd1 TIP3PFBOX 9.5 iso
addions fsd1 Cl- 5
saveAmberParm fsd1 fsd1.prmtop fsd1.crd
savepdb fsd1 fsd1.pdb
#
# tleap -s -f leap.script
#