You shouldn't need to change any plugins unless you want to - nothing I posted there is specific to that crafting plugin.
That's a good start -
none of the files in your game should have spaces in the filenames, so that's something you might want to check now. If you get to the point where you try to distribute the game to other people, spaces and special characters can cause a variety of bugs.
For the error, try replacing the plugin code with this. I only changed a portion but figured replacing the whole body was easier than describing which portion to edit.
Code:
Game_Party.prototype.loseItem = function(item, amount, includeEquip) {
if (!DataManager.isIndependent(item))
{
this.gainItem(item, -amount, includeEquip);
return;
}
var group, found=0;
if (item.etypeId!=undefined)
group=item.etypeId==0 ? this.weapons() : this.armors();
else
group=this.items();
switch (item._dataClass)
{
case 'item':
group=this.items();
break;
case 'weapon':
group=this.weapons();
break;
case 'armor':
group=this.armors();
break;
}
for (var i=0; i<group.length; i++)
{
if (!group[i])
continue;
if (group[i].baseItemId && group[i].baseItemId==item.id)
{
found++;
this.removeIndependentItem(group[i], includeEquip);
if (found==amount)
break;
}
}
};