Hi Jason and Mike,
@ Jason i think you have a similar problem that i face on my machine(for some weird reason), this is what i need to do to set this error right on my C18 students version.
Like Mike said, do(install in the default C directory)
Project>Set Language Tool Locations>Microchip C18 Toolsuite>Default Search Path & Directories>
Set include search path to. C:\MCC18\h
Set Library search path to. C:\MCC18\lib
This is normal, now here is the twist, when ever i install c18 after a new copy of windows. I need to do this for the first project that i make using it.
Project>Build Options>Directories....
In the Drop down menu "Show directories for", set locations for both the include and library search paths mentioned above.Here is a picture of this second part.