If this error arises  - Error - could not find file 'c018i.o' when you try to compile using C18, you need to add the path to the library. Under Project>Build Option>Project, In the build option change the "Show directory for" to Library Search Path and add a new path to the path of C18 LIB folder. In my case its shown as C:\MCC18\LIB. The below 2 screens shots below show the solution for the c018i.o Error. With this the program should be able to compile without any problem.