Hi jahc,
There doesn't seem to be a lot of information on the LBN_SORT method at all.
However, it seems that you are supplying the pointer to the gadget for the lbs_GInfo field when it needs to be a GadgetInfo structure.
Either that, or you are supplying the GadgetInfo structure as the first argument to DoGadgetMethod() when you actually need to supply a pointer to the ListBrowser gadget object. The wrong information being supplied to one (or both) of these parameters is likely to be causing you some trouble.
I couldn't find the info to confirm it, but I reckon you are most likely right in passing 0 as the lbs_Column argument.