I think it's ok with code. Here is working code with my spreadsheet:
<iframe width='300' height='500' frameborder='0' src='https://docs.google.com/spreadsheet/ccc?key=1_E95obcIyHPRdblORhNqzbLRTz2Oo17TntFXXv7El14&usp=sharing&single=true&range=A1%3AB36&output=html&widget=true&rm=minimal'></iframe>
Problem is with sharing permission. Check this out.