this install error is returned from FGT that this URL is not a support format, but if config on FMG side is like this for a while, looks weird that after upgrade FMG to 5.2.6 then see this install error
for can not delete that "Access Granted" on FMG side, may because of the space in the name, FMG 5.2.4 or earlier still allow to create name with space, but in 5.2.6 we added syntax check to follow FOS side logic which does not allow space in the name (I tested on 5.2.5)
v8c # conf webfilter ftgd-local-rating
v8c (ftgd-local-rating) # ed "a a"
node_check_object fail! for url a a
value parse error before 'a a'
Command fail. Return code -257
v8c (ftgd-local-rating) # ed "a.a"
new entry 'a.a' added
but may cause delete issue for upgraded config, I will double check this case, and see if can run script to delete this entry from backend db