Different users cannot use my WinForms app at the same time

Question

I have a VS WinForms app that uses OleDB to read (only reading, no writing) info from an Excel file. My end-users install the program via click-once, created through the publish-option in Visual Studio Community. The installation works fine. BUT: Only one user at a time is able to use the program. Windows gives me this error:

Files that may help descibe the problem:
  C:\Users\shoo\AppData\Local\Temp\WERA825.tmp.WERInternalMetadata.xml
  C:\Users\shoo\AppData\Local\Temp\WERDFAA.tmp.appcompat.txt
  C:\Users\shoo\AppData\Local\Temp\WERE18F.tmp.mdmp

The files all contain the same information:

I have done the following to help avoid the error:

I only read the Excel file and have made the actual Excel file read-only.
I close all my connections directly after filling my datasets or using my readers.
A WinForms app without OleDB and distributed through publish>click-once works for multiple users at the same time.
If I start a new project, copy/paste all my code(so it is exactly the same, but the app-name is different): Two instances of my program can be run at the same time...

This is my first C# experience, so please be gentle ;-)

TheDanMan · Accepted Answer

I think the problem is that when you open an excel file, it creates a "lock". Normally if you do this via the MS Excel interface, it will prompt you with a warning and you can choose what to do See here. But in this case, since you're reading it from a C# program, it might be returning that weird error

I suggest you try storing the main file on a network drive and make a copy of it locally to the application folder for each user to use their own file instead of reading the same file at once. See here for file copying

Try the following code

string filename = "Streetlife Product Database.xlsx";
string fullfilename = String.Format(@"//MILKYWAY/SO_Arc/template/{1}", Application.StartupPath, filename);
string tempath = System.IO.Path.GetTempPath();
string filenameTemp = String.Format("{0}.xlsx", System.IO.Path.GetTempFileName());
System.IO.File.Copy(fullfilename, filenameTemp, true);
string connetionString = String.Format(@"Provider = Microsoft.ACE.OLEDB.12.0; Data Source ={0};Extended Properties = ""Excel 12.0 Xml;HDR=YES;IMEX=1""", filenameTemp);

using (OleDbConnection oledb = new OleDbConnection(connetionString))
{
    try
    {
        oledb.Open();
    }
    catch (Exception ex)
    {
        oledb.Close();
        oledb.Dispose();

        MessageBox.Show("Error trying to read file: " + ex.Message);                    
    }
 }

Different users cannot use my WinForms app at the same time

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