It's the version of MPLINK that doesn't match the C18 compiler version used to compile ifi_library.o
"Due to a change in COFF file format, MPLAB C18 v3.00 and later will
not be compatible with versions of MPLINK prior to v4.00"
The original ifi_library.o was compiled with C18 v2.4.
Kevin did provide an updated version of the ifi_library.o compiled under C18 v3.
Look in the workspace directory for Kevin's project and you should see both:
- ifi_frc_8722_24.lib
- ifi_frc_8722_30.lib
In your MPLAB project file list under "Library Files" one of these two files will be listed. You probably just need to swap to the other file. Click on the name in the file list and delete, then go to Project -> Add Files to Project... and browse to the file you want to use. When browsing you'll need to specify "Files of type: Library Files (*.lib)"