Can also be a CPU issue. It is not available for arm-linux and x86_64 linux only i386, afaik.
Check if the package graph is installed in /usr/local/lib/fpc/<version>/units/<platform>
If it isn't then graph is not supported
In my case /usr/local/lib/fpc/3.1.1/units/arm-linux does not contain graph because it is not supported on arm.