W/o having a formula, it's impossible to determine how much fat you have. However, i'm going to guestimate that you've got about 25% cocoa fat in there - which is low. To tom's point, one of your issues may be that it's simply not enough fluidity for the unit to grind efficiently, and you're going to have to find a way to further fluidize it - either via some lecithin or additional fat. It's my guess that you're low enough in fat that lecithin's not going to get you to where you need to be, so you're prob looking at additional fat. Now, i'd not monkey around with veg fats. Unless you know what you're doing, there's a very high likelihood that you're going to very quickly run into something called eutectics, which will give you all sorts of troubles should you want to temper this. Rather, i'd look to add cocoa butter. Now, yo'uve got two options:
1) add pure cocoa butter, bring the total fat up to, oh, say 35%. Or, if you don't have access to cocoa butter
2) remove the contents of your grinder, and add more roasted nibs. Liquify those nibs - they'll have an approximate fat content of, lets say 52%. Once you create you fluid chocolate liquor, slowly add in your original paste batch, using the fluidity from the extra liquor to assist with the grinding. 0.2% fluid lecithin will also help at this point.