(this problem may only apply if using separate source and build directories)
after I updated with subversion, the version banner was not correct, still reflecting version from the prior installation
1. first check whether the version file is in fact old
cat $SOURCE_DIR/src/nrnoc/nrnversion.h
2. if so you must remove it and recompile, ie
cd $SOURCE_DIR
rm src/nrnoc/nrnversion.h
cd $BUILD_DIR/src/nrnoc
make
cd $BUILD_DIR
make install
(seems like I had to do make twice before nrnversion.h came into existance)