> there shouldn't be such a random behavior in a
> computer program!  Could it be a time out issue in
> communications with the server?
You can set the timeout in the options.
More likely your getting problems with a fast/multi-core machine and 3.4x 

3.4x was a multi-thread attempt and has many problems.
Try 3.32 <http://forum.httrack.com/readmsg/17840/17833/index.html>