Steve,
I think that this is most likely an Apache not running/accessible issue (even though it says that it seems to be running in the log).
Now you have an aborted installation, you should have the apache load there on you system - can you start it manually and using a browser get to http://<servername> - you should get an "it works message"?
If not, then investigate your Apache logs as to why apache is not starting / accessible.
If Apache does appear to start and be working OK when tested manually, it would suggest that it is an issue with the PSI not being able to start Apache, or that it can start Apache OK, but the PSI can't reach it to test that it is there.
A possible quick and dirty solution might be to start Apache manually just before it gets to this part of the install.
You could also try running the PSI with Apache already started before running the PSI.
Another thought - I presume that there is not another Apache installation on the machine that might be confusing things with the PSI?
See how you go with that
Rgds
Gary