Adena Bug Problem

I dont know if im doing it right. My server doesn't seem to have weight limit and i tried doing that thief keys trick in elf village cos the npc at TI is screwy. I first at 1 mil keys then 2 mil keys and the price turns negative at 3mil. Then i keep adding and subtracting till the price is within my adena range. I have 5k a and i got it to 704 adena. However when i press "buy", the notice comes up and says that i have insufficient adena ;( I dunno if im doing it wrong