[Q] Help needed in syncing source topic

Im trying to sync cm12's source code fro git hub
im using virtualbox on host windows 8.1
the virtual machine is ubuntu 14.xx
this porbably the 20th time i did a

Code:

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repo sync

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it always used to get stuck (it got interupted one way or another :c )
anyways ...later I finally made it till here

HTML Code:

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Fetching projects: 100% (546/546), done. 
Traceback (most recent call last):
  File "/home/bass_face/.repo/repo/main.py", line 506, in <module>
    _Main(sys.argv[1:])
  File "/home/bass_face/.repo/repo/main.py", line 482, in _Main
    result = repo._Run(argv) or 0
  File "/home/bass_face/.repo/repo/main.py", line 161, in _Run
    result = cmd.Execute(copts, cargs)
  File "/home/bass_face/.repo/repo/subcmds/sync.py", line 681, in Execute
    project.Sync_LocalHalf(syncbuf)
  File "/home/bass_face/.repo/repo/project.py", line 1230, in Sync_LocalHalf
    lost = self._revlist(not_rev(revid), HEAD)
  File "/home/bass_face/.repo/repo/project.py", line 2309, in _revlist
    return self.work_git.rev_list(*a, **kw)
  File "/home/bass_face/.repo/repo/project.py", line 2503, in rev_list
    p.stderr))
error.GitError: CyanogenMod/android rev-list ('^ddc4820db2658b6779caf9946e787098d6007967', 'HEAD', '--'): fatal: bad object HEAD

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and i got this error can someone please guide me...and i did search for many possible solutions...nothing seems to be related to this porblem or is left unanswered, please help or atleast direct me to a proper solution

many thanks ^_^

xda-developers