[yocto] bitbake error

[idealsim]

Hi, i'm trying to build an image with Yocto on a new machine (ubuntu 16.04  
LTS)but i have this error that i can't resolve. Can you help ?

ERROR: Execution of event handler 'uninative_event_fetchloader' failed
Traceback (most recent call last):
   File  
"/home/b/yocto-krogoth/sources/poky/meta/classes/uninative.bbclass", line  
55, in uninative_event_fetchloader(e=<bb.event.BuildStarted object at  
0x7f2015027790>):
              if not os.path.exists(tarballpath):
     >            bb.utils.mkdirhier(tarballdir)
                  if d.getVar("UNINATIVE_URL", True) == "unset":
   File "/home/b/yocto-krogoth/sources/poky/bitbake/lib/bb/utils.py", line  
716, in  
mkdirhier(directory='/home/b/yocto-krogoth/../../yocto/downloads//uninative/acf1e44a0ac2e855e81da6426197d36358bf7b4e88e552ef933128498c8910f8'):
              if e.errno != errno.EEXIST:
     >            raise e

OSError: [Errno 13] Permission denied: '/home/b/yocto-krogoth/../../yocto'

ERROR: Command execution failed: Traceback (most recent call last):
   File "/home/b/yocto-krogoth/sources/poky/bitbake/lib/bb/command.py",  
line 104, in runAsyncCommand
     commandmethod(self.cmds_async, self, options)
   File "/home/b/yocto-krogoth/sources/poky/bitbake/lib/bb/command.py",  
line 325, in buildTargets
     command.cooker.buildTargets(pkgs_to_build, task)
   File "/home/b/yocto-krogoth/sources/poky/bitbake/lib/bb/cooker.py", line  
1423, in buildTargets
     bb.event.fire(bb.event.BuildStarted(buildname, ntargets), self.data)
   File "/home/b/yocto-krogoth/sources/poky/bitbake/lib/bb/event.py", line  
178, in fire
     fire_class_handlers(event, d)
   File "/home/b/yocto-krogoth/sources/poky/bitbake/lib/bb/event.py", line  
110, in fire_class_handlers
     execute_handler(name, handler, event, d)
   File "/home/b/yocto-krogoth/sources/poky/bitbake/lib/bb/event.py", line  
82, in execute_handler
     ret = handler(event)
   File  
"/home/b/yocto-krogoth/sources/poky/meta/classes/uninative.bbclass", line  
55, in uninative_event_fetchloader
     bb.utils.mkdirhier(tarballdir)
   File "/home/b/yocto-krogoth/sources/poky/bitbake/lib/bb/utils.py", line  
716, in mkdirhier
     raise e
OSError: [Errno 13] Permission denied: '/home/b/yocto-krogoth/../../yocto'