Qubes builder fails to build vmm-xen for fc32 dom0

I copied qubes-os-r4.1.conf to create builder.conf, and deleted all lines in the COMPONENTS section, except vmm-xen. Then I make get-sources and make vmm-xen, but it threw out this error:

Makefile.generic:45: *** Building packages for fc32 not supported by any of configured plugins.  Stop.

How can I fix the problem so that I can build vmm-xen ? Any help is appreciated.

Interestingly , when I delete builder.conf and repeat the process the third time, the error mysteriously gone. Sorry for the disturbance.

I guess the reason is that I ran./setup beforehand, and it somehow made something bad.