First, try updating the binaries (update both i386 and amd64 if you are not sure which) of Wkhtmltopdf in install/binary/pdf/linux from
http://code.google.com/p/wkhtmltopdf/. Make sure the file execution permission is still on after the update.
If this doesn't help then try updating your Linux packages (these were for CentOS but you should have similar packages):
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yum install libXext.i386
yum install libXfont.i386
yum update freetype.i386
yum install a2ps.i386
yum install urw-fonts libXext openssl-devel
yum install libX11-devel.i386
yum install libXfont-devel.i386
yum install libXt
yum install bitmap-fonts bitmap-fonts-cjk bitstream-vera-fonts
yum install dejavu-lgc-fonts fontconfig-devel fonts-ISO8859-2 fonts-ISO8859-2-100dpi fonts-ISO8859-2-75dpi fonts-KOI8-R fonts-KOI8-R-100dpi fonts-KOI8-R-75dpi
yum install fonts-arabic fonts-bengali fonts-chinese fonts-gujarati fonts-hebrew fonts-hindi fonts-japanese fonts-kannada fonts-korean fonts-malayalam fonts-oriya fonts-punjabi fonts-sinhala fonts-tamil fonts-telugu
yum install libXfontcache
yum install tetex-fonts
yum install xorg-x11-fonts-100dpi xorg-x11-fonts-75dpi xorg-x11-fonts-ISO8859-1-100dpi xorg-x11-fonts-ISO8859-1-75dpi xorg-x11-fonts-ISO8859-14-100dpi xorg-x11-fonts-ISO8859-14-75dpi xorg-x11-fonts-ISO8859-15-100dpi xorg-x11-fonts-ISO8859-15-75dpi xorg-x11-fonts-ISO8859-2-100dpi xorg-x11-fonts-ISO8859-2-75dpi xorg-x11-fonts-ISO8859-9-100dpi xorg-x11-fonts-ISO8859-9-75dpi xorg-x11-fonts-Type1 xorg-x11-fonts-base xorg-x11-fonts-cyrillic xorg-x11-fonts-ethiopic xorg-x11-fonts-misc xorg-x11-fonts-syriac xorg-x11-fonts-truetype
yum install libXrender
yum install gettext-devel expat-devel curl-devel zlib-devel openssl-devel
yum groupinstall "X Window System"
yum groupinstall Graphics
yum groupinstall "Development Libraries"
yum install gd-devel.i386
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Installing these packages ensures Wkhtmltopdf has all the libraries and fonts it needs.
If all fails then you should consider our PDF web service. Any TODCM site can utilize our web service to generate all PDF documents; your server needs internet access to utilize this service. Please let me know if you need this service.
David