compile error

Built target roots_example
make[2]: *** No rule to make target 'doc/docbook/system/man1/en/./pix-png.valid', needed by 'share/doc/html/man1/en/pix-png.html'.  Stop.
CMakeFiles/Makefile2:56012: recipe for target 'doc/docbook/system/man1/en/CMakeFiles/pix-png_man1_HTML.dir/all' failed
make[1]: *** [doc/docbook/system/man1/en/CMakeFiles/pix-png_man1_HTML.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
Linking C executable ../../../bin/adrt_master
[ 51%] Built target adrt_master
Linking C executable ../../bin/lgt
[ 51%] Built target lgt
Makefile:147: recipe for target 'all' failed
make: *** [all] Error 2