This is a documented issue with Google Chrome (http://code.google.com/p/chromium/issues/detail?id=103618).

The issue only occurs when you use a comma in a file name that is uploaded.

To resolve, reupload the file, but without the comma in the file name.
Note:  With the case of auto-generated PDF files, such as Online Reenrollment and Online Admissions Forms, or eReceipts, you will need to make sure the Part or Form name contains no commas.

OR

Use another supported browser.