Catastrophic error: cannot open source file "os.h" Blackfin ADP-BF527 Processor


I have a project file which has the ethernet drivers loaded along with the Lwip(RTOS). I have enabled both the external memory and heap memory sufficiently to support this implementation. 

However, when I try to build the project, I get the following error: 

Catastrophic error: cannot open source file "os.h" 
I checked that under the projects properties -> C/C++ Build->Settings, on the left panel, -> Tool Settings->CrossCore Blackfin C/C++ Compiler->Preprocessor, on the right, the "Additional include directories" box should contain:



These were added under the "include" but when you expand the "include" folder on the main view of croscore, the uCOS-III and uC-CPU appear greyed out, such thing that could imply that they don't exist or they are not linked anywhere... 

Has anyone encountered this before? 

Your help is greatly appreciated by a fellow engineer.