PDFBox Problem

Hello experts,
i am using a PDFBox-0.7.3 to read PDF files and parse it to a text,but suddenly i found that some of the PDFs are not read by the PDFBox-0.7.3,and when i looked at the non-read files i found that the only diffrence between the read files and the unread files are that:
The PDF producer which in the case of the unread files is : Acrobat distiller v9.0 and later.it gives me the : Object reference not set to an instance of an object exception.

else the PDF parser works great.

Any ideas ?
thanks