(I see no depots here, just an archive lib.)
>ar: libpwplus.a not in archive format
You need to remove this file and start fresh.
>You mean I delete libpwplus.a file
Yes, remove it and then make.
In fact your archive lib make rule should have that rm there:
libpwplus.a: cfckpw.o ...
rm -f $@
ar cru $@ cfckpw.o ...