CCS/TM4C123BE6PM: Cannot open source file lwip/opt.h

Part Number:TM4C123BE6PM

Tool/software: Code Composer Studio

I am building an existing project based on TM4C123BE6PM. but the compiler gives the following error:  Cannot open source file lwip/opt.h

I am working with Code Composer Studio Version: 7.3.0.00019 and  with compiler version TIv16.9.4.LTS.

The Tivaware library version is 2.1.4.178.

I attach the screenshot concerning the configuration of the ARM COMPILER and of the ARM LINKER search path.

I have also tried to build the project by physically importing the folder lwip present in ti\TivaWare_C_Series-2.1.4.178\third_party\lwip-1.4.1\src\include\lwip      but the compiler gives the same error

What I am missing?

Thanks in advance