You have to add the need payload on Pylons declaration in Lua file
check any Su30MK entry Mod (Su-30MKI.lua) for example , search for Pylons you can find Astra/Brahmos and KAB500S
I am and other in 2.7 without this kind of problem.
sorry but I don't think that's the Error, cuez lot of people use the same MOD, perhaps you have an other MOD causing the problem, try the MOD alone in Mods folder just to confirm.
Regrds