Error when running chm2pdf

[Suyash]

I got the following error when I ran chm2pdf to convert a chm file to
pdf using

chm2pdf --book ???????.chm

Here is the message displayed on terminal. Can someone tell me what
could be wrong and how to fix it.

Traceback (most recent call last):
File "/usr/bin/chm2pdf", line 1108, in <module>
main(sys.argv)
File "/usr/bin/chm2pdf", line 1102, in main
convert_to_pdf(cfile, filename, outputfilename, options)
File "/usr/bin/chm2pdf", line 318, in convert_to_pdf
objective_urls=get_objective_urls_list(filename)
File "/usr/bin/chm2pdf", line 121, in get_objective_urls_list
urls_list.append(spline[5])
IndexError: list index out of range