I'm seeing something similar.

Server: 1.13
Client: 1.14.1
Protocol: bzr://

In my case it happens when my VPN is down and my upstream sends back Admin Prohibited packets.

Backtrace:

bzr: ERROR: bzrlib.errors.TooManyConcurrentRequests: The medium '<bzrlib.smart.medium.SmartTCPClientMedium object at 0x949aa8c>' has reached its concurrent request limit. Be sure to finish_writing and finish_reading on the currently open request.

Traceback (most recent call last):
  File "/usr/lib/python2.6/dist-packages/bzrlib/commands.py", line 727, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/commands.py", line 922, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.6/dist-packages/bzrlib/commands.py", line 559, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python2.6/dist-packages/bzrlib/builtins.py", line 2878, in run
    exclude=safe_relpath_files(tree, exclude))
  File "/usr/lib/python2.6/dist-packages/bzrlib/decorators.py", line 192, in write_locked
    result = unbound(self, *args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/workingtree_4.py", line 226, in commit
    result = WorkingTree3.commit(self, message, revprops, *args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/decorators.py", line 192, in write_locked
    result = unbound(self, *args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/mutabletree.py", line 228, in commit
    *args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/commit.py", line 308, in commit
    self._check_bound_branch(possible_master_transports)
  File "/usr/lib/python2.6/dist-packages/bzrlib/commit.py", line 449, in _check_bound_branch
    possible_master_transports)
  File "/usr/lib/python2.6/dist-packages/bzrlib/decorators.py", line 138, in read_locked
    result = unbound(self, *args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/branch.py", line 2280, in get_master_branch
    possible_transports=possible_transports)
  File "/usr/lib/python2.6/dist-packages/bzrlib/branch.py", line 134, in open
    possible_transports=possible_transports)
  File "/usr/lib/python2.6/dist-packages/bzrlib/bzrdir.py", line 807, in open
    return BzrDir.open_from_transport(t, _unsupported=_unsupported)
  File "/usr/lib/python2.6/dist-packages/bzrlib/bzrdir.py", line 842, in open_from_transport
    return format.open(transport, _found=True)
  File "/usr/lib/python2.6/dist-packages/bzrlib/bzrdir.py", line 1918, in open
    return self._open(transport)
  File "/usr/lib/python2.6/dist-packages/bzrlib/bzrdir.py", line 2890, in _open
    return remote.RemoteBzrDir(transport, self)
  File "/usr/lib/python2.6/dist-packages/bzrlib/remote.py", line 111, in __init__
    response = self._call('BzrDir.open', path)
  File "/usr/lib/python2.6/dist-packages/bzrlib/remote.py", line 55, in _call
    return self._client.call(method, *args)
  File "/usr/lib/python2.6/dist-packages/bzrlib/smart/client.py", line 129, in call
    result, protocol = self.call_expecting_body(method, *args)
  File "/usr/lib/python2.6/dist-packages/bzrlib/smart/client.py", line 142, in call_expecting_body
    method, args, expect_response_body=True)
  File "/usr/lib/python2.6/dist-packages/bzrlib/smart/client.py", line 87, in _call_and_read_response
    readv_body=readv_body, body_stream=body_stream)
  File "/usr/lib/python2.6/dist-packages/bzrlib/smart/client.py", line 42, in _send_request
    protocol_version)
  File "/usr/lib/python2.6/dist-packages/bzrlib/smart/client.py", line 112, in _construct_protocol
    request = self._medium.get_request()
  File "/usr/lib/python2.6/dist-packages/bzrlib/smart/medium.py", line 690, in get_request
    return SmartClientStreamMediumRequest(self)
  File "/usr/lib/python2.6/dist-packages/bzrlib/smart/medium.py", line 906, in __init__
    raise errors.TooManyConcurrentRequests(self._medium)
TooManyConcurrentRequests: The medium '<bzrlib.smart.medium.SmartTCPClientMedium object at 0x949aa8c>' has reached its concurrent request limit. Be sure to finish_writing and finish_reading on the currently open request.

bzr 1.14.1 on python 2.6.2 (linux2)
arguments: ['/usr/bin/bzr', 'commit', '-m', ' move populate_dashboard_columns to tracker controller']
encoding: 'UTF-8', fsenc: 'UTF-8', lang: 'en_AU.UTF-8'
plugins:
  builddeb             /usr/lib/python2.6/dist-packages/bzrlib/plugins/builddeb [unknown]
  bzrtools             /usr/lib/python2.6/dist-packages/bzrlib/plugins/bzrtools [1.14]
  launchpad            /usr/lib/python2.6/dist-packages/bzrlib/plugins/launchpad [unknown]
  netrc_credential_store /usr/lib/python2.6/dist-packages/bzrlib/plugins/netrc_credential_store [unknown]
  rebase               /usr/lib/python2.6/dist-packages/bzrlib/plugins/rebase [0.4.4]
  svn                  /usr/lib/python2.6/dist-packages/bzrlib/plugins/svn [0.5.4]
*** Bazaar has encountered an internal error.
    Please report a bug at https://bugs.launchpad.net/bzr/+filebug
    including this traceback, and a description of what you
    were doing when the error occurred.