In this entry I will show how you can create a Microsoft Excel file using .Net.
// Create the Excel Application object.
ApplicationClass ExcelApp = new ApplicationClass();
// Set the visibility of the application.
ExcelApp.Visible = true;
// Create a new Excel Workbook.
Workbook ExcelWorkbook = ExcelApp.Workbooks.Add(Type.Missing);
// Create a new Excel Sheet.
Worksheet ExcelSheet = (Worksheet)ExcelWorkbook.Sheets.Add(ExcelWorkbook.Sheets.get_Item(1), Type.Missing, 1, XlSheetType.xlWorksheet);
try
{
// Loop for 10 rows.
for (int rwCount = 1; rwCount <= 10; rwCount++)
ApplicationClass ExcelApp = new ApplicationClass();
// Set the visibility of the application.
ExcelApp.Visible = true;
// Create a new Excel Workbook.
Workbook ExcelWorkbook = ExcelApp.Workbooks.Add(Type.Missing);
// Create a new Excel Sheet.
Worksheet ExcelSheet = (Worksheet)ExcelWorkbook.Sheets.Add(ExcelWorkbook.Sheets.get_Item(1), Type.Missing, 1, XlSheetType.xlWorksheet);
try
{
// Loop for 10 rows.
for (int rwCount = 1; rwCount <= 10; rwCount++)
{
// Loop for 3 columns.
for (int clmCount = 1; clmCount <= 3; clmCount++)
{
ExcelSheet.Cells[rwCount, clmCount] = "This is Row - " + rwCount + " Column - " + clmCount;
}
}
// Save the Excel sheet.
// The @ symbol makes the string to contain any special characters inside the string without breaking the string.
ExcelApp.Save(@"C:\Projects\Ex.xls");
}
b. Select ASP.NET Web Site as the template, select C# as the language, and give a file system location and a name (prjFirst) for the project before pressing Ok. 
c. Now we need to add a page to write our code. To do that, right click on top of the project and click on Add New Item.... 
e. Now you need to use the required web controls and write the code required in the appropriate files. For this demonstration I will put a label and a button only. When the button is clicked I will display a greeting message in the label. 
h. Now build and see if the page is having any errors. If no errors step one is done. 
b. Select Class Library as the template under C# project type and give a location and a name (clFirstWebPart) before clicking Ok. 
c. Right click and delete the Class1.cs file since we would like to create a new class with a meaningful name. 
then select Class as the template and give an appropriate name (csFirstWebPart.cs) and click Add. 
e. Now you need to refer System.Web namespace. To do so right click on project and click ok Add Reference..., then select the System.Web and click Ok. 
f. After inheriting the class from the WebPart override the CreateChildControls method to create a user control and load the user control we create earlier in step 1. 
g. Now build the project by right clicking on project and selecting Build. If no errors occur then that means we have completed step 2 as well. 
ii. Go to the root folder of the web site (C:\Inetpub\wwwroot). Now find the folder named UserControls and paste the copied two files there. 
Notes – 
· If the UserControls folder doesn’t exist you can create it there. 
ii. Go to the root folder of the web site (C:\Inetpub\wwwroot). Now find the folder named bin and paste the copied file there. 
Notes – 
· If the bin folder doesn’t exist you can create it there. 
b. Click on Web Parts under Galleries in the Site Settings page to open the Web Part Gallery. 
c. In the web part gallery page you will see all the added web parts. But not our one. So we need to add that here. To do this click on New button. 
Note – 
e. Now our new web part will appear in the Web Part Gallery. This is enough but it is always better to change some properties of the web part. So open up the web part property page by clicking on the Edit button. 
f. Remember that we need to test the web part before we add it to a web page. To do this simply click on the web part. 
g. If you are also having the default settings then you will definitely get an error of request for the permission of type.... This is because we didn’t change the SharePoint trust level. To change this I will use the easy way of changing the trust level in the configuration file to full though the best way is to create a trust file. 
Do an IISReset and refresh the internet explorer page. Now the web part will be displayed to you.
b. Now on any web part zone click ‘Add a Web Part’ button. 
c. Among all the web parts listed select the web part that we have created (First Web Part), select the check box in front of it and click the Add button. 
You will see the web part appearing on the page. 
e. Click on ‘Click Me’ button and see the output. 
Even though adding a new web part was bit of a process, after adding doing changes to it is not that difficult. What you have to do is change the ascx and ascx.cs files and copy the new ones to the UserControls folder. I have simply changed the message to a new one using this method.
Have you seen Microsoft's latest Live product? Its named as Live Mesh. 
4. Press Ok to save the change. 
This error is due if the 
