I am going to assume the file is being accessed in an Asp.Net web application, and that the file resides in the web application child folders. I am going to paste in some sample C# code to help debug common issues. I am adding trace events that can be read using trace.axd in asp.net.

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string path = System.Web.HttpContext.Current.Request.MapPath("/graphics/");
if (System.IO.Directory.Exists(path) == false)
{
//Folder path doesn't exist
System.Web.HttpContext.Current.Trace.Warn("path",path);
System.Web.HttpContext.Current.Trace.Warn("Folder path doesn't exist");
return;
}

path = System.Web.HttpContext.Current.Request.MapPath("/graphics/ + imageURL);
if (System.IO.File.Exists(path) == false)
{
//File does not exist
System.Web.HttpContext.Current.Trace.Warn("path",path);
System.Web.HttpContext.Current.Trace.Warn("File does not exist");
return;
}

System.Drawing.Image originalImage = System.Drawing.Image.FromFile( path );
.
.
.

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Just a word of warning some methods of System.Drawing.Image uses unmanaged GDI+ handles, and on a busy site can easily exceed the pool of these handles. Depending how often they are used and disposed of.

Your code should work, I just tested the following in my work network, and it loaded the image fine.

Dim imageURL As String = "\\SERVERNAME\Share\Test\Untitled.jpg"
Dim originalImage As System.Drawing.Image = System.Drawing.Image.FromFile(imageURL)

- What does your imageURL string contain at the point of loading the Image. (the reason being you have called it 'imageURL', is it a url?)

- Does your website (the Network Service user) have the correct permissions for this folder?

And, as Ocean10000 says, I would do the processing within a Try...Finally block (disposing of the Image in 'Finally' to free up resources)