I have given xpath also.... Still it is throwing error as
"The test run cannot continue due to an unrecovarable error."
Cannot identify the Object "Sel_Date" (of class WebButton)
Verify that this object's Properities match an object currently displayed in your application.
Calendar is a complex object to automate, unless it is a straight forward three drop downs for Day,year and month
You would have to write functions to convert a given date to 'months', 'day' and 'year' for eg: 10/5/2016 should give us
10-October - Oct
5 - 5(Day 5 of october)
2016 - year 2016
Now you would have to created descriptions for each entity for your UI. Start with year, month and date.
If description matches click on that object. Basically it should work like below
Select year 2016 - (Collections of years)
Select month October (Collections of months)
Select day 5.(Collections of Days)
The above solution should work for any date you give to function.
The above is just a hint on how I would approach the situation. To get more specific response, you would have to share details of how your UI looks.