I have claimed Kathleen Davis as a dependent why not this year?

Really?  This is a "community" forum.  How the hell would you think anybody knows who the hell Kathleen Davis is to you?  Did you actually expect someone at TT to look at last years return and then tell you why the change?  You got to be kidding me!  That being said, what is her relationship to you?  How old is she?  How much money does she make?  Is she a full time student?  ... Go look up the rules for dependents on the IRS website!

Since we can't see your return, we need a little more help to determine why the software isn't allowing your dependent this year.  

Sometimes it is simply a question that has been answered incorrectly in the interview such as "Did Kathleen provide more than half of her own support?"  

I suggest revisiting the section My Info (Personal Info in some versions) and reviewing these questions.  You can also double-check if she is eligible outside of the software with this helpful IRS tool: Interactive Tax Assistant: Dependents.