Your group is currently "mkgroup".  This indicates that neither
your gid nor your pgsid (primary group associated with your SID)
is in /etc/group.

The /etc/group (and possibly /etc/passwd) files should be rebuilt.
See the man pages for mkpasswd and mkgroup then, for example, run

mkpasswd -l [-d] > /etc/passwd
mkgroup  -l [-d] > /etc/group

Note that the -d switch is necessary for domain users.

NetWare@DONARUMO-NETWK ~
$ cd c:\twlsdk

NetWare@DONARUMO-NETWK /cygdrive/c/twlsdk
$ cd build

NetWare@DONARUMO-NETWK /cygdrive/c/twlsdk/build
$ cd demo
bash: cd: demo: No such file or directory

NetWare@DONARUMO-NETWK /cygdrive/c/twlsdk/build
$ cd demos

NetWare@DONARUMO-NETWK /cygdrive/c/twlsdk/build/demos
$ make
cygwin warning:
  MS-DOS style path detected: C:\TwlSDK/build/buildtools/commondefs
  Preferred POSIX equivalent is: /cygdrive/c/TwlSDK/build/buildtools/commondefs
  CYGWIN environment variable option "nodosfilewarning" turns off this warning.
  Consult the user's guide for more details about POSIX paths:
    http://cygwin.com/cygwin-ug-net/using.html#using-pathnames
/bin/sh: -c: line 0: syntax error near unexpected token `('
/bin/sh: -c: line 0: `cygpath -u C:/Program Files (x86)/Freescale/CW for NINTEND
O DSi V1.6 SP2/'
/bin/sh: -c: line 0: syntax error near unexpected token `('
/bin/sh: -c: line 0: `cygpath -u C:/Program Files (x86)/Freescale/CW for NINTEND
O DSi V1.6 SP2/'
==== /cygdrive/c/twlsdk/build/demos/gx/UnitTours/DEMOLib
/bin/sh: -c: line 0: syntax error near unexpected token `('
/bin/sh: -c: line 0: `cygpath -u C:/Program Files (x86)/Freescale/CW for NINTEND
O DSi V1.6 SP2/'
/bin/sh: -c: line 0: syntax error near unexpected token `('
/bin/sh: -c: line 0: `cygpath -u C:/Program Files (x86)/Freescale/CW for NINTEND
O DSi V1.6 SP2/'
make[3]: *** No rule to make target `/ARM_Tools/Command_Line_Tools/mwccarm.exe',
 needed by `/cygdrive/c/TwlSDK/build/buildtools/twl/verinfo.cw.cc'.  Stop.
true && cp -rf /cygdrive/c/TwlSDK/include/twl.h /cygdrive/c/TwlSDK/cache/include
/twl.h.16M.A9.ARM.CW.CWVER-1.ISTD.REL.TS.TWL.LTD.C.h && (cd /cygdrive/c/TwlSDK/c
ache/include/ && rm -rf /cygdrive/c/TwlSDK/cache/include/twl.h.16M.A9.ARM.CW.CWV
ER-1.ISTD.REL.TS.TWL.LTD.C.mch  && rm -rf /cygdrive/c/TwlSDK/cache/include/twl.h
.16M.A9.ARM.CW.CWVER-1.ISTD.REL.TS.TWL.LTD.C.depend && "/ARM_Tools/Command_Line_
Tools/mwccarm.exe" -DSDK_16M -DSDK_ARM9 -DSDK_CODE_ARM -DSDK_CW -DSDK_CW_MAJOR_V
ER=1 -DSDK_LINK_ISTD -DSDK_RELEASE -DSDK_TS -DSDK_TWL -DSDK_TWLLTD -lang c -proc
 arm946e -nothumb -nopic -nopid -interworking -O4 -inline on,noauto -opt speed -
g -msgstyle std -w all -enc SJIS -char signed -stdinc -enum int -stdkeywords off
 -Cpp_exceptions off  -gccinc -I. -I'C:/TwlSDK/include' -I'C:/PROGRA~2/INTELL~1/
IS-TWL~1/Target/include/ARM9' -MD -precompile twl.h.16M.A9.ARM.CW.CWVER-1.ISTD.R
EL.TS.TWL.LTD.C.m C:/TwlSDK/cache/include/twl.h.16M.A9.ARM.CW.CWVER-1.ISTD.REL.T
S.TWL.LTD.C.h) && mv /cygdrive/c/TwlSDK/cache/include/twl.h.16M.A9.ARM.CW.CWVER-
1.ISTD.REL.TS.TWL.LTD.C.m /cygdrive/c/TwlSDK/cache/include/twl.h.16M.A9.ARM.CW.C
WVER-1.ISTD.REL.TS.TWL.LTD.C.mch && ((echo /cygdrive/c/TwlSDK/cache/include/twl.
h.16M.A9.ARM.CW.CWVER-1.ISTD.REL.TS.TWL.LTD.C.mch: /cygdrive/c/TwlSDK/include/tw
l.h \\; sed -e '1d' -e "/ARM_EABI_Support/d;s/\\x0D//g;s!\\([A-Za-z]\\):[\\\\\/]
!/cygdrive\\/\\l\\1\\/!g;s/\\([^ ]\\)\\\\\([^ ]\\)/\\1\\/\\2/g;" /cygdrive/c/Twl
SDK/cache/include/twl.h.16M.A9.ARM.CW.CWVER-1.ISTD.REL.TS.TWL.LTD.C.d) > /cygdri
ve/c/TwlSDK/cache/include/twl.h.16M.A9.ARM.CW.CWVER-1.ISTD.REL.TS.TWL.LTD.C.dep
&& mv /cygdrive/c/TwlSDK/cache/include/twl.h.16M.A9.ARM.CW.CWVER-1.ISTD.REL.TS.T
WL.LTD.C.dep /cygdrive/c/TwlSDK/cache/include/twl.h.16M.A9.ARM.CW.CWVER-1.ISTD.R
EL.TS.TWL.LTD.C.depend && rm -rf /cygdrive/c/TwlSDK/cache/include/twl.h.16M.A9.A
RM.CW.CWVER-1.ISTD.REL.TS.TWL.LTD.C.d /cygdrive/c/TwlSDK/cache/include/twl.h.16M
.A9.ARM.CW.CWVER-1.ISTD.REL.TS.TWL.LTD.C.h)
/bin/sh: /ARM_Tools/Command_Line_Tools/mwccarm.exe: No such file or directory
make[3]: *** [/cygdrive/c/TwlSDK/cache/include/twl.h.16M.A9.ARM.CW.CWVER-1.ISTD.
REL.TS.TWL.LTD.C.mch] Error 127
make[2]: *** [build_for_ltd_arm] Error 2
make[1]: *** [build-twl] Error 2
make: *** [make-sub-p-pre] Error 2

NetWare@DONARUMO-NETWK /cygdrive/c/twlsdk/build/demos
$