Actually there are two factions lahori Ahmedis which I dont think believe in the prophet hood of Mirza Ghulam Ahmed Qadiani & then there is another faction that consider him as a prophet... The argument they often use that holy prophet Hazrat Muhammad PBUH represents the seal of Nabowat (Khatem-o-Nabieen) but Risalat does not ends at Our Holy Prophet... The argument against this from the Muslim Ulema is that one cannot be a Rasool without being a Nabi, but can be a Nabi & not be a Rasool,(yes there is a difference b/w Rasool & Nabi while there were 124,000 Nabis only 313 amongst them were Rasools) therefore Khatim-e-Nabowat of Our holy prophet Hazrat Muhammad PBUH means that any one claiming to be a rasool after him is an imposter and a false prophet.
I must say that no one in the Ummah can be more guided then the Four Rightly Guided Caliphs.
Now Syedna Abu Bakr launched a campaign against the imposter who claimed to be Nabi after the demise of Prophet Mohammad (PBUH).. so if there was a hint of new prophet, then these Rightly guided Caliphs might have accepted them or atleast should have given them a chance to prove their claim.
But we didn't see any thing of this sort, even in the middle ages, there were several imposters claiming to be the prophets but none of them was acknowledged by the Ulemas of that time and were considered Dajaal and Fitna...
So how come this person can be a Prophet.. the discussion of Nabi and Rasool is thing of later stage...