OK, non-standard ports, so it is bound to be related to this.
"So yes, I am using non-standard ports for the Apache server, 8001 for http and 8020 for https."
How come you are mentioning https at installation time - this would normally configured post installation?
Presumably, at this point (of installation) your Apache is still configured as http and hence the PSI should be looking for a http server on port 8001 - is that correct?
check the site.xconf and psi_ii.xml files for the correct non-standard ports that you are using.
Worst case scenario, install it as port 80 and then change the site.xconf and httpd.conf files to use the non-standard port...
Rgds
Gary