The sour taste is most likely due to bacterial growth in the meat. How, when, and why that took place is the variable. It could have been that the deer was allowed to hang at warm temperature too long and the meat started to spoil prior to processing. Or it could have been allowed to warm up too much during processing or during the thawing of the meat you used for the jerky.
       You didn't say if the jerky tasted sour right after it was made or after you had it for period of time. If it was bad right away then the problem was most likely due to the handling prior to making your jerky. However, if it happened some time after it was made then my guess is that it was not dried/smoked long enough and it still had enough moisture to allow bacterial growth.
    Vacuum packaging or freezing your jerky is another way to retard bacterial growth.
    You best bet is to analyze what could have been different about this batch compared to the others. Is it possible that you thawed to meat out but forgot about it for a day or two before making it?

Dave & Ruth
D & R Processing