Update 02/22/07: Loweded Wookie was kind enough to reply to this post and provide me with a explanation as to why this issue exists. Apparently, the Finder writes out a file named .DS_Store in each directory that it touches. According to this site, the .DS_Store file serves the following purpose:
The .DS_Store files are created by the Finder during its normal course of operation but they are invisible by default. The Finder will automatically put a .DS_Store file into every folder you have opened. These files are used to save the positions of icons, the size of the respective Finder window, the window’s background, and many more view options. While professional users consider the .DS_Store files to be a design flaw of the Mac OS X Finder, a mechanism like this is necessary when opening Finder windows for exchangeable disk media to give former users of the classic Mac OS the same user experience they had in previous operating system versions. If you don’t like to see the .DS_Store files, replace the Finder by a better file management application
This explains why I am unable to open a file if other files are being copied into the same directory. I really appreciate the fact that Loweded took some time out of his day to research this issue with me. It truly was driving me nuts. I don’t necessarily agree with how OS X does this however, at least now I understand why I received the error mentioned below.
Just today I noticed that OS X doesn’t seem let me open a file that I just copied if there are more files that still need to be copied. For example, I tried to copy ~ 280 Megs worth of videos off of my computer upstairs.

When I tried to open one of the files which was already copied I received the following error:

Am I doing something wrong or has Apple just not figured this one out?
Update 2/19/07: Somebody over at digg didn’t believe me that this was a problem so I decided to try it out again when I got home from work. As you can see from these screenshots it is a problem. When I tried and open an image which already had a thumbnail generated for it, OS X told me it couldn’t access the file. This is driving me nuts. Am I doing something wrong?
For this test I copied six JPEGs:
I then tried to open one of the JPEGs which already had a thumbnail generated for it:

