Cannot open Excel file in C#

Question

I have the following C# function in my project, which is supposed to open and return an existing Excel workbook object:

Application _excelApp;

// ...

private Workbook OpenXL(string path, string filename)
{
    try
    {
        if (_excelApp == null)
        {
            _excelApp = new Application();
        }

        Workbook workBook = _excelApp.Workbooks.Open(path + filename,   // Name
                                                     0,                 // Do not update links
                                                     true);             // Open read-only

        return workBook;
    }
    catch (Exception e)
    {
        _excelApp = null;
        throw new ArgumentException("Error opening " + path + filename, e);
    }
}

But when I run it with "C:\" and "scratch.xlsx", the Open() call throws the following error:

Microsoft Excel cannot access the file 'C:\scratch.xlsx'. There are several possible reasons:

• The file name or path does not exist.
• The file is being used by another program.
• The workbook you are trying to save has the same name as a currently open workbook.

The file and path does exist: I have copied the path from the error message and pasted it into a command window and the file loads up in Excel. The file is not locked: Excel can open it fine but my program cannot, even straight after a reboot. I am not trying to save it, I am trying to open it so the last option is irrelevant.

I am at a loss to understand why this simple piece of code is not working. Any suggestions would be hugely appreciated.

[edit] I have now tried opening that file from my personal network drive (M:) and from a USB stick. All to no avail.

The application is actually a Windows service, running under the local system account and generating reports. It currently write CSV reports with no access problems whatsoever. I am now trying to get it to open an excel file as a template report and fill in various fields. It is when opening the Excel file that it fails. I am thinking that the administrator account option everyone is suggesting is a red herring since it can write CSV files wityh no problem. [/edit]

--- Alistair.

Answer 1

I found the following page:

http://social.msdn.microsoft.com/Forums/en-US/b81a3c4e-62db-488b-af06-44421818ef91/excel-2007-automation-on-top-of-a-windows-server-2008-x64

Where it says that...

it’s not supported to automate office products UI less. It seems that Windows Server 2008 and Excel 2007 enforce the given statement.

The questioner then describes exactly the situation I am in with a Windows Service that cannot open an Excel file, although the same code in a command-line program has no problem.

The response advises to create the following folder:

Windows 2008 Server x64: C:\Windows\SysWOW64\config\systemprofile\Desktop

Windows 2008 Server x86: C:\Windows\System32\config\systemprofile\Desktop

I have tried this and it worked a treat! Can anyone explain why it is needed and any downsides?

Thanks,

--- Alistair.

Answer 2

Run the program as admin, the C:/ cannot be accessed by a program unless the user is running as admin. You can make your program prompt the user it must be run as admin by altering the ApplicationManifest: How do I force my .NET application to run as administrator?