ASP.Net Error: Failed conversion from nvchar to DATETIME

Dear Programmer, I have a data column named year and have data type DATETIME

Year DATETIME NULL

aspx.cs

DATETIME MyYr = DATETIME.NOW;
string Yr = MyYr.DATETIME.ToString("yy")
//yy= 18 (2018)

But when we execute this query than we have got a error as like - 

Error datatype failed conversion from nvchar to DATETIME.

Note - Please help me out.