Acrobat and/or Reader Error “.tmp” when using fdf

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I'm populating PDF's via FDF (& php) and for the most part it works fine however some users are getting either a "Acrobat cannot open "Acrxyz.tmp" (or a "Reader cannot open "xyz.tmp", in some cases). I've found info about possible causes surrounding: apache "MOD-Deflate", IE Cache and Volatile memory & "fdf_close" among other things..some config info: it's on apache 2 with (the Mod_deflate module), I don't have fdftk installed so can't do much about fdf_close. the fdf is called with an include. and these are all through https SSLUsers are on IE anywhere from IE 6 to IE 8 most using acrobat 8 or Reader 8.x or 9.2most users get the pdf without a problem but.... any suggestions to help narrow my search to server setting user-config etc. or solutions would be helpful?here's the header info if that helps // Header is required for explorer to send this file to Acrobat Viewer header ("Content-Type: application/vnd.fdf"); // Prevent caching header("Cache-Control: post-check=0, pre-check=0", false); header("Pragma: public");Thanks!