Cant join a friends lobby pvz gw2

for the past few weeks i havent been able to join my friends lobbys, we both play on pc, i live in the uk and he lives in spain, we play on the europe server (used to) but then we couldnt join each others partys, and got the error, "there was a problem accepting the invite" even if i tried to join him, no luck. the only fix was switching servers to the na east or smth, which makes the game unplayable and too laggy. Please help!!