If you are using vpopmail 5.4.30 and you get this error

client_connect:_warning:_config_begin_failed/Aack,_child_crashed._(#4.3.0)/

or

client connect: warning: config begin failed/Aack, child crashed. (#4.3.0)

maybe you have to try this:

cat > ~vpopmail/etc/vusagec.conf << __EOF__
Server:
Disable = True;
__EOF__

In this way you could correct the error and save your strength for something better.