When running samrdump.py in BT5, I am getting the below error. I checked all over and found the time issue is not related, and am currently using the most up to date code. Any suggestions on how to correct?

I stripped out the address and found domains(x's y's) because they are irrelevant to the error.

root@bt:/pentest/python/impacket-examples# python samrdump.py 192.168.x.x
Retrieving endpoint list from 192.168.x.x
Trying protocol 445/SMB...
Found domain(s):
 . xxxxxx
 . yyyyyy
Looking up users in domain xxxxx
Protocol failed: 
Traceback (most recent call last):
  File "samrdump.py", line 182, in <module>
  File "samrdump.py", line 66, in dump
    entries = self.__fetchList(rpctransport)
  File "samrdump.py", line 142, in __fetchList
    resp = rpcsamr.enumusers(domain_context_handle)
  File "/usr/lib/pymodules/python2.6/impacket/dcerpc/samr.py", line 697, in enumusers
    retVal = SAMRRespEnumDomainUsersHeader(data)
  File "/usr/lib/pymodules/python2.6/impacket/dcerpc/samr.py", line 472, in __init__
    if aBuffer: self.load_header(aBuffer)
  File "/usr/lib/pymodules/python2.6/impacket/ImpactPacket.py", line 256, in load_header
    hdr_len = self.get_header_size()
  File "/usr/lib/pymodules/python2.6/impacket/dcerpc/samr.py", line 498, in get_header_size
    assert var_size > 0