Can not store files in Document Libraries

We're running Sitefinity 6.2.4900.  We can create Document Libraries, but when I try to upload a document via drag-and-drop or clicking on the link to choose a file from my hard drive, it fails.  The pink progress bar fills up then I get an error.

I have tried a document library that uses the database storage provider and also the file system.  I created the file system store in "~/App_Data/Storage/Documents" and tested it, which passed.  Both database and file system store behave exactly the same by displaying an alert and showing an exclamation point by the name of the document.  I have tried multiple document types - jpg, pdf, docx, etc.

If I hit the [OK] button on the error alert then look in the document library, I see an entry for the failed document, but it is zero bytes.

I just ran a test upgrade of Sitefinity to 8.2, and the same issue exists in the upgraded site.

There is nothing in the ~/App_Data/Sitefinity/Logs directory.  I don't know where to look to see if Sitefinity is throwing an error.  I look in the IIS logs and I see what appears to be a 500 Server error.

I would appreciate any help on figuring this out.  We'd like to use the Document storage to store PDFs that we link to in our site and this appears to be a good way to handle it.

Attached are some screenshots.  The IIS Log Entry is below my name.

Thanks,
-Brian E. Parker

2015-11-06 22:25:55 172.17.1.41 POST /Telerik.Sitefinity.Html5UploadHandler.ashx - 443 - 10.60.27.230 Mozilla/5.0+(Windows+NT+6.1;+WOW64)+AppleWebKit/537.36+(KHTML,+like+Gecko)+Chrome/46.0.2490.80+Safari/537.36 oursite.ourdomain.com/.../UploadDialog 500 22 50 0