Error: 'nmake' is not recognized as an internal or external command, operable program or batch file
This error message is because either you do not have the correct supported compiler installed or you have launched FLUENT using the "FREE" compiler with the SDK and you are not launching FLUENT from the Microsoft Visual Studio C + + Command Prompt window first.
If you are using the "FREE" version and the SDK make sure that you are using the 64-bit (x64) compiler tools with Visual Studio. When you open the compiler command window make sure it reports "Setting environment for using Microsoft Visual Studio x64 tools" something like what it shown below. It you do not see x64 tools in the command window then you are using a 32-bit compiler and you will not be able to complile FLUENT 64-bit UDFs.
Verify that you have installed the 64-bit Compiler Tools
Windows XP 64-bit
Control Panel, Add/Remove Programs, Select Microsoft Visual Studio 2008 Standard or Professional Edition and click the Change/Remove button. This will bring you into Maintenance Mode. Choose Add/Remove Features. Add X64 Compilers and Tools.
Control Panel, Programs and Features, Select Microsoft Visual Studio 2008 Standard or Professional Edition application then choose Uninstall/Change. This will bring you into Maintenance Mode. Select C++ then check X64 Compilers and Tools.