how to solve

Question

Hi all,i could not able to solve the problem

Object reference not set to an instance of an object.

i an uploading an excel and it calculates the values and gives the output for one filename which in compatibility mode.after uploading another file it gives the following error

..please help

Server Error in '/' Application.

Object reference not set to an instance of an object.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

Line 642: finally

Line 643: {

Line 644: workbook.Close(Missing.Value, Missing.Value, Missing.Value);

Line 645: application.Quit();

Line 646: this.releaseObject(xlWs);

Source File: c:\Users\ccbt\Desktop\PPDM_TEST_HITVALIDATION_MODULE\SECONDARY_VALUES_STORAGE\SECONDARY_VALUES_STORAGE\test123.aspx.cs Line: 644

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.]

SECONDARY_VALUES_STORAGE.test123.GetExcel(String fileName) in c:\Users\ccbt\Desktop\PPDM_TEST_HITVALIDATION_MODULE\SECONDARY_VALUES_STORAGE\SECONDARY_VALUES_STORAGE\test123.aspx.cs:644

SECONDARY_VALUES_STORAGE.test123.btnUpload_Click_Click(Object sender, EventArgs e) in c:\Users\ccbt\Desktop\PPDM_TEST_HITVALIDATION_MODULE\SECONDARY_VALUES_STORAGE\SECONDARY_VALUES_STORAGE\test123.aspx.cs:208

System.Web.UI.WebControls.Button.OnClick(EventArgs e) +9553594

System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +103

System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10

System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13

System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +35

System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1724