The syntax of the command is incorrect. POD validation failed! Documentation will not be written. Checking if your kit is complete... Looks good Note (probably harmless): No library found for -lXtst Note (probably harmless): No library found for -lXext Note (probably harmless): No library found for -lX11 Writing Makefile for X11::GUITest Microsoft (R) Program Maintenance Utility Version 6.00.8168.0 Copyright (C) Microsoft Corp 1988-1998. All rights reserved. cp GUITest.pm blib\lib\X11\GUITest.pm C:\cpanrun\build\5-10-0\bin\perl.exe C:\cpanrun\build\5-10-0\lib\ExtUtils\xsubpp -typemap C:\cpanrun\build\5-10-0\lib\ExtUtils\typemap -typemap typemap GUITest.xs > GUITest.xsc && C:\cpanrun\build\5-10-0\bin\perl.exe -MExtUtils::Command -e mv GUITest.xsc GUITest.c cl -c -I/usr/X11R6/include -I/usr/X/include -Wall -O2 -DVERSION=\"0.21\" -DXS_VERSION=\"0.21\" "-IC:\cpanrun\build\5-10-0\lib\CORE" -DNDEBUG -DX11_GUITEST_ALT_L_FALLBACK_META_L GUITest.c Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 12.00.8804 for 80x86 Copyright (C) Microsoft Corp 1984-1998. All rights reserved. Command line error D2021 : invalid numeric argument '/Wall' NMAKE : fatal error U1077: 'cl' : return code '0x2' Stop.