ftplib throws: IndexError: tuple index out of range

[Antoon Pardon]

I have written a small backup program, that uses ftplib to make
remote backups. However recentely the program starts to regularly
raise IndexErrors, as far as I can see the problem is in socket.py
Can anyone shed some light?

This is the traceback:

Traceback (most recent call last):
  File "/usr/local/lib/python-apps/rmtdump/pymain.py", line 93, in main
    Exit_Nr = process(sys.argv)
  File "/usr/local/lib/python-apps/rmtdump/rmtdump.py", line 228, in program
    process(path)
  File "/usr/local/lib/python-apps/rmtdump/rmtdump.py", line 170, in process
    of = rmt.open(rmtsep.join([rmt5lcl(rt), archive]), "wb")
  File "/usr/local/lib/python-apps/rmtdump/ftputil.py", line 198, in open
    return ftpfile(ftp, fn, mode, True)
  File "/usr/local/lib/python-apps/rmtdump/ftputil.py", line 69, in __init__
    self.cnct =  self.ftp.transfercmd("%s %s" % (cmd, rfn))
  File "/usr/lib/python2.7/ftplib.py", line 376, in transfercmd
    return self.ntransfercmd(cmd, rest)[0]
  File "/usr/lib/python2.7/ftplib.py", line 693, in ntransfercmd
    conn, size = FTP.ntransfercmd(self, cmd, rest)
  File "/usr/lib/python2.7/ftplib.py", line 339, in ntransfercmd
    resp = self.sendcmd(cmd)
  File "/usr/lib/python2.7/ftplib.py", line 249, in sendcmd
    return self.getresp()
  File "/usr/lib/python2.7/ftplib.py", line 215, in getresp
    resp = self.getmultiline()
  File "/usr/lib/python2.7/ftplib.py", line 201, in getmultiline
    line = self.getline()
  File "/usr/lib/python2.7/ftplib.py", line 186, in getline
    line = self.file.readline(self.maxline + 1)
  File "/usr/lib/python2.7/socket.py", line 478, in readline
    if e.args[0] == EINTR:
IndexError: tuple index out of range

Locals by frame, innermost last

Frame main in /usr/local/lib/python-apps/rmtdump/pymain.py at line 111
           backtrace = <function backtrace at 0x7ff8c5d36230>
                  pn = 'rmtdump'
             process = <function program at 0x7ff8c5d361b8>

Frame program in /usr/local/lib/python-apps/rmtdump/rmtdump.py at line 261
             aborted = True
                argv = ['/usr/local/sbin/rmtdump']
                path = '/home'

Frame process in /usr/local/lib/python-apps/rmtdump/rmtdump.py at line 190
                b_rt = '/home'
          backupflag = 'r--'
         backupstamp = 1453021366
          checkstamp = 1450374304
                dirs = ['antoon', 'jenny', 'lost+found', 'photo']
             entries = ['0-home', 'antoon', 'homelady', 'jenny', 'lost+found', 'photo', 'recover']
               entry = 'recover'
            fileinfo = posix.stat_result(st_mode=16877, st_ino=2490369, st_dev=2058L, st_nlink=5, st_uid=0, st_gid=0, st_size=4 ...
               files = []
                fqpn = '/home/recover'
              islink = <function islink at 0x7ff8c9073500>
             ismount = <function ismount at 0x7ff8c9073758>
                last = 1455445804.979914
               newfn = 'home/!2016-01-17 at 10_02_46-tbz'
                 now = 1455445804
         nr_of_tries = 0
                  of = None
               oldfn = 'home/!ENTRY-tbz'
                path = '/home'
                  rt = '/home'
               stamp = '1450374304'
               start = 1455445804
              timefn = '!2016-01-17 at 10_02_46-tbz'
               tryal = 1
              update = True

Frame open in /usr/local/lib/python-apps/rmtdump/ftputil.py at line 198
                  fn = 'home/!ENTRY-tbz'
                 ftp = <ftputil.FTP instance at 0x7ff8c5d3add0>
                mode = 'wb'
                self = <ftputil.FTP instance at 0x7ff8c5d3acf8>

Frame __init__ in /usr/local/lib/python-apps/rmtdump/ftputil.py at line 69
               bound = True
                  ch = 'b'
                 cmd = 'STOR'
                  cn = <ftputil.FTP instance at 0x7ff8c5d3add0>
               count = 1
                mode = 'wb'
                 rfn = 'home/!ENTRY-tbz'
                self = None

Frame transfercmd in /usr/lib/python2.7/ftplib.py at line 376
                 cmd = 'STOR home/!ENTRY-tbz'
                rest = None
                self = <ftplib.FTP_TLS instance at 0x7ff8c5d4c878>

Frame ntransfercmd in /usr/lib/python2.7/ftplib.py at line 693
                 cmd = 'STOR home/!ENTRY-tbz'
                rest = None
                self = <ftplib.FTP_TLS instance at 0x7ff8c5d4c878>

Frame ntransfercmd in /usr/lib/python2.7/ftplib.py at line 352
                 cmd = 'STOR home/!ENTRY-tbz'
                conn = <socket._socketobject object at 0x7ff8c5d2d2f0>
                host = '192.110.0.54'
                port = 64649
                rest = None
                self = <ftplib.FTP_TLS instance at 0x7ff8c5d4c878>
                size = None

Frame sendcmd in /usr/lib/python2.7/ftplib.py at line 249
                 cmd = 'STOR home/!ENTRY-tbz'
                self = <ftplib.FTP_TLS instance at 0x7ff8c5d4c878>

Frame getresp in /usr/lib/python2.7/ftplib.py at line 215
                self = <ftplib.FTP_TLS instance at 0x7ff8c5d4c878>

Frame getmultiline in /usr/lib/python2.7/ftplib.py at line 201
                self = <ftplib.FTP_TLS instance at 0x7ff8c5d4c878>

Frame getline in /usr/lib/python2.7/ftplib.py at line 186
                self = <ftplib.FTP_TLS instance at 0x7ff8c5d4c878>

Frame readline in /usr/lib/python2.7/socket.py at line 478
                 buf = <cStringIO.StringO object at 0x7ff8c5d40298>
             buf_len = 0
                   e = timeout()
                self = <socket._fileobject object at 0x7ff8c7b75b50>
                size = 8193