设置日期选择器上选择的日期值

I'm trying to get a date picker on my asp.net webpage. I've been able to run the same code using a master page and it works, but now I'm trying to get it to work without a master pager and I'm getting error message: Error: Unable to get value of the property 'aspnetForm.ctl00_txtDOB': object is null or undefinedI'm trying to get a date picker on my asp.net w