I'm having problems with "./build.sh -O /usr/obj -T /usr/tools" command,
trying to build the system.

I've retrieve the entire source tree at /usr, I'm not updating anything.
The DESTDIR is set to /NetBSD-current.

What can I do to solve this problem?

Error:

bash-2.05# ./build.sh -O /usr/obj -T /usr/tools

(...)

obj ===> sys/arch/i386/stand/netboot
obj ===> sys/arch/i386/stand/netboot/3c509
nbmake:
"/usr/src/sys/arch/i386/stand/netboot/3c509/../../Makefile.booters" line
27: warning: Couldn't exec "cd
/usr/src/sys/arch/i386/stand/netboot/3c509/../../../../..//arch/i386/stand/genprom
&& /usr/tools/bin/nbmake -V .OBJDIR"
Could not fork

nbmake: stopped in /usr/src/sys/arch/i386/stand/netboot/3c509
*** Error code 2

Stop.
nbmake: stopped in /usr/src/sys/arch/i386/stand/netboot
*** Error code 1

Stop.
nbmake: stopped in /usr/src/sys/arch/i386/stand
*** Error code 1

Stop.
nbmake: stopped in /usr/src/sys/arch/i386
*** Error code 1

Stop.
nbmake: stopped in /usr/src/sys/arch
*** Error code 1

Stop.
nbmake: stopped in /usr/src/sys
*** Error code 1

Stop.
nbmake: stopped in /usr/src
*** Error code 1

Stop.
nbmake: stopped in /usr/src

ERROR: failed to make build
*** BUILD ABORTED ***
bash-2.05#