Too Many PDF Files Open

I have an AIR app developed in Flash CS5.5 that opens PDFs using HTMLLoader. After opening about 50 PDFs I get an error dialog that says, "The maximum number of files are already open..." The PDFs don't look like they are opened because I clear the htmlloader each time to load the new PDF. How can I get rid of this error? I want the user to be able to open an unlimited number of PDFs.  How do you close a file opened by HTMLLoader? This is with AIR 2.6 and Reader 10.1.