Download popup not coming properly in asp.net page load - asp.net

Question

I am trying to open the file based on the below code.
I am not using server.mappath. because, the access path is direct file server path and it is mapped with service account.
protected void Page_Load(object sender, EventArgs e)
{
string filePath1 = #"\\RMN\T001\PROC\MATERIALDB\";
Response.Clear();
Response.ClearContent();
Response.ClearHeaders();
Response.Buffer = true;
Response.AddHeader("content-disposition", "attachment; filename=" + "MAT01210821.png");
Response.WriteFile(filePath1);
Response.ContentType = "";
Response.End();
}
I am getting below error.
The filename, directory name, or volume label syntax is incorrect.
My requirement is, when i execute the above code, it should ask popup to end user "Do you want to open or save the file ..."? below screenshot for reference.
enter image description here

Answer 1

Even though the actual error is missing, the line Response.WriteFile(filePath1); is trying to use a folder as if it was a file.
To avoid such confusion, the folder path should be stored in a variable named folder and used to construct the actual path.
var folder = #"\\RMN\T001\PROC\MATERIALDB\";
var fileName="MAT01210821.png";
var filePath=Path.Combine(folder, fileName) ;
...
Response.AddHeader("content-disposition", "attachment; filename=" + fileName);
Response.WriteFile(filePath);