Maybe not a GUI problem, but:
Code:
iacopo@Iacopo:~/Desktop$ pdfreflow book.pdf
Converting PDF to XML
Traceback (most recent call last):
File "/usr/bin/pdfreflow", line 8, in <module>
load_entry_point('calibre==0.4.72', 'console_scripts', 'pdfreflow')()
File "build/bdist.linux-i686/egg/calibre/ebooks/lrf/pdf/reflow.py", line 419, in main
File "build/bdist.linux-i686/egg/calibre/ebooks/lrf/pdf/reflow.py", line 378, in __init__
File "build/bdist.linux-i686/egg/calibre/ebooks/lrf/pdf/reflow.py", line 365, in generate_xml
calibre.ebooks.ConversionError: /bin/sh: pdftoxml.exe: command not found