Works fine using my custom date types and format but Warning keeps on appearing

In Regional and language >> Date and Time , I created a new format using this format string l,F j,Y which displays Thursday,November 28,2013 and also create a new date type and assign it with this format.I configure the clock using this date type.

It works and looks good but this warning comes out:

Warning: key() expects parameter 1 to be array, boolean given in _clock_get_date_format() (line 213 of /home/public_html/mysite/sites/all/modules/clock/clock.module).

What are the possible cause of this problem and the solutions?

I'm looking forward for your response.Thank you.