Thanks for your suggestions, Tony and Andreas. I rebuilt julia so that versioninfo() gave
Julia Version 0.3.3-pre+78 Commit 75b347b (2014-11-19 10:23 UTC) Platform Info: System: Linux (x86_64-linux-gnu) CPU: Intel(R) Core(TM) i7-3770 CPU @ 3.40GHz WORD_SIZE: 64 BLAS: libblas LAPACK: liblapack LIBM: libopenlibm LLVM: libLLVM-3.3 but that did not fix the problem. However, by editing Make.user so that the system blas, lapack etc are no longer used, and rebuilding again, I seem to have fixed the problem; versioninfo() now gives Julia Version 0.3.3-pre+78 Commit 75b347b (2014-11-19 10:23 UTC) Platform Info: System: Linux (x86_64-linux-gnu) CPU: Intel(R) Core(TM) i7-3770 CPU @ 3.40GHz WORD_SIZE: 64 BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY Sandybridge) LAPACK: libopenblas LIBM: libopenlibm LLVM: libLLVM-3.3 Still, it is curious that the PyPlot error did not happen every time (it was maybe 2 times out of 3). Anyway, thanks again for your help.
