Can't open pdf report

I set up a SS User Usage by Day report which gets delivered to my e-mail as a pdf file.  I had been able to open them.  Lately, however, I get an Adobe Reader error:  "There was an error opening this document.  The root object is missing or invalid."  I'm using Reader 9.2, which I've reinstalled.  I can open other pdfs just fine w/ Reader 9.2.  Did the report generation mechanism change somehow?