On distcc master machine, libpng version is 1.5.10; on slave machine, libpng version is 1.2.10. emerging dev-lang/R in distcc-pump results in runtime error from libpng as "compiled with 1.2.10 but linked against 1.5.10" disabling distcc-pump works. Somehow master machine did not send png.h to slave, and the latter used png.h from itself.
1) Please post your `emerge --info' output in a comment. 2) Please attach the entire build log to this bug report.