[Zope] PDF files in Zope 2.6

We recently upgraded from Zope 2.5 to 2.6 and are experiencing a problem with PDF's loading via the browser (any) plugin. The Adobe plugin loads in the browser and the user is presented a blank screen, as the content is either not sent or received properly. This problem does not occur with all PDF files, however the ones that are being affected did work with the prior version of Zope. Does anybody have knowledge of the cause of this problem or where/if a fix can be obtained. Also if the pdf's in question are downloaded rather than sent to the browser, the content comes accross fine. TIA, Jason