Hi Indrajeet,
What is the datetime value passed to the DB?
Even though the column is of Datetime type it may not accept all dateformats.
More over value from Dateteime.Now should be converted to string. This might the exception you are receiving not actual date insert issue.
Check this
http://msdn.microsoft.com/en-us/library/8kb3ddd4.aspx[
^] for more about Datetime.Now usage.
Also you can debug and check the value assigned to objBusinessUI.LastLogIn and then manually insert that value via SSMS and can trace the probelm easily.