I have narrowed the problem down further and suffered several Windows blue screen events in the process. The hang happens when a subprocess is invoked to complete a defvar while loading libraries. The compile library invokes find to determine how best to use find and grep. pcl-cvs invokes cvs to obtain its version. I have determined that the fork succeeds and also the execve. I'm still too confused by the subprocess support to get much futher. The Cygwin strace does seems to show that the SIGCHLD cannot be delivered. One other interesting observation is that this does not happen with 21.4.8 Windows [3]. Both are using the same package hierarchy. I'm hoping this relates to some of the other subprocess problems that are seen in 21.5 david