So... I have in my user-config.jam: using msvc : 14.1 : "M:/Compilers/VC2017/VC/Tools/MSVC/14.10.25017/bin/HostX64/x64/cl.exe" ; And this did work at one point, but both with latest develop and master I now get: M:/data/boost/boost/tools/build/src/tools\msvc.jam:1103: in configure-really *** argument error * rule generate-setup-cmd ( version : command : parent : options * : cpu : global-setup ? : default-global-setup-options : default-setup ) * called with: ( 14.10.25017 14.10.25017 : M:/Compilers/VC2017/VC/Tools/MSVC/14.10.25017/bin/HostX64/x64 : M:\Compilers\VC2017\VC\Tools\MSVC\14.10.25017\bin\HostX64 : <command>M:\Compilers\VC2017\VC\Tools\MSVC\14.10.25017\bin\HostX64\x64\cl.exe <command>M:/Compilers/VC2017/VC/Tools/MSVC/14.10.25017/bin/HostX64/x64/cl.exe : i386 : : x86 : vcvars32.bat ) * extra argument 14.10.25017 M:/data/boost/boost/tools/build/src/tools\msvc.jam:811:see definition of rule 'generate-setup-cmd' being called M:/data/boost/boost/tools/build/src/tools\msvc.jam:201: in configure M:/data/boost/boost/tools/build/src/tools\msvc.jam:153: in msvc.init M:/data/boost/boost/tools/build/src/build\toolset.jam:43: in toolset.using M:/data/boost/boost/tools/build/src/build\project.jam:1052: in using C:\cygwin64\home\John\user-config.jam:46: in modules.load M:/data/boost/boost/tools/build/src\build-system.jam:249: in load-config M:/data/boost/boost/tools/build/src\build-system.jam:389: in load-configuration-files M:/data/boost/boost/tools/build/src\build-system.jam:524: in load M:\data\boost\boost\tools\build\src/kernel\modules.jam:295: in import M:\data\boost\boost\tools\build\src/kernel/bootstrap.jam:139: in boost-build M:\data\boost\boost\boost-build.jam:17: in module scope Anyone any ideas? Thanks, John. --- This email has been checked for viruses by AVG. http://www.avg.com