nmake means there isn't an external compiler (typically Microsoft). I'm not sure why the built in compiler is failing though, does it run when you launch Fluent outside of Workbench. The lack of parallelisation of the code may mean the result isn't correct but doesn't normally stop the compiler from working.https://forum.ansys.com/discussion/comment/92417#Comment_92417

@Rob, I used Build-In Compiler and also tried both inside Workbench and outside workbench. I'm getting error 'C:\PROGRA~1\ANSYS' is not recognized as an internal or external command, operable program or batch file. Where is this directory of 'C:\PROGRA~1\ANSYS' tho?.I'm not sure warning should be ignore? but if I continue to Load it, it will become Error: The UDF library you are trying to load (libudf) is not compiled for parallel use on the current platform (win64).The system cannot find the file specified.