Military ties between the two countries have been governed officially by an arms embargo imposed by Britain on Argentina.
There is not longer an arms embargo imposed by Britain on Argentina.
this is new information about the future so should be marked neither but the AI is only taking what is written in the passage so marked it incorrect.
( z1 embargo :ARG0 ( z2 country :name ( z3 name :op "Britain" ) ) :ARG1 ( z4 arm ) :ARG2 ( z5 country :name ( z6 name :op "Argentina" ) ) :time ( z7 no-longer ) )