I just tracked down the source of the `Cannot create a process' error.
This is seems to be a bug in WordPerfect.

The FIFO mentioned in your ktrace output is used to communicate with
the WP print daemon.  When `xwp' tries to open the FIFO for writing
and fails, it forks another process to start the daemon.  The error is
displayed because `wpexc60' exits with a status of 1, indicating
failure.  The reason it fails is that it tries to open the FIFO with
O_RDWR (which doesn't make sense), apparently expecting it to be
equivalent to opening it with O_RDONLY|O_NDELAY but leaving the FIFO
in blocking mode, and instead gets EINVAL.

I suppose we could kluge around this in the FIFO code, but I'm not
convinced that's a good idea.