500 Server Error During Uploads

I'm running into an odd problem that I can't seem to track down.  I'm hoping someone else may have experienced something similar and can help.

I recently upgraded our web server and it is now running PHP v5.3.10-1ubuntu3.19.  This, plus the update to MySQL v5.5.4400 were really the only changes to the server.

Most of the sites are running fine, but one in particular is giving me some problem when I try and upload files.  These could be PDF or JPG.  The really odd thing is that I will get the error with one PDF file, but can upload another with no problems.  In the case of trying to upload images, I get the error if I try to upload an image, but not if I try and upload a PDF.

I have attached an image of the error message I am getting.  I have tried to rename the files with no luck.  I am running CMSB 2.63.  It was on a much older version and I thought that may be the problem, but upgrading CMSB made no difference.

Any thoughts will be greatly appreciated.  This is the first time I've run into something like this.  I do not see any errors in the Apache logs to help me track down the root of the problem.

pcolvin