Exception information:
Exception type: NullReferenceException
Exception message: Object reference not set to an instance of an object.
at clsGlobal.ResetPassword(String Login_Id)
at NEXOLIMS.Account.frmFrgetPsswrd.btnChngPwd_Click(Object sender, EventArgs e)
at DevExpress.Web.ASPxButton.OnClick(EventArgs e)
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
It's a common exception that means your code is trying to access/reference an object that has not been instanced, and it's a null object that doesn't exist in memory.
You are also being told where it is happening the exception. You need to use the debugger and set a breakpoint in the class method and single-step until it blows up and use Quickwatch to find out what object on the line that threw the exception is null. You find out why the object is null.