Issue while opening INPs

[Skulldron]

Hello,
I got problem with opening some of input files. While opening some of inp's i got following traceback:

Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\DEV\Python\lib\tkinter\__init__.py", line 1699, in __call__
    return self.func(*args)
  File "D:/DEV/Work Directory/APP.py", line 655, in load_network
    self.network = Network(self.network_filepath)
  File "C:\DEV\Python\lib\site-packages\epynet-0.1-py3.6.egg\epynet\network.py", line 20, in __init__
    self.ep.ENopen(self.inputfile, self.rptfile, self.binfile)
  File "C:\DEV\Python\lib\site-packages\epynet-0.1-py3.6.egg\epynet\epanet2.py", line 76, in ENopen
    raise ENtoolkitError(self, ierr)
epynet.epanet2.ENtoolkitError: File Error 302: cannot open input file.

Process finished with exit code 0

I know its related with the Programmers Toolkit, could you please give me some hints how to solve this as a novice to programming? Thank you very much in advance :)

EDIT: For all you guys, who might deal with that kind of error, the reason may be related to the name of the file or .inp file, for instance when name contains some diacritics like ę, ś, ą etc. But some .inps do not work anyway for no reason.