Why would a page that is one click off a PR5 homepage be a PR-zero, other than the issue of it being a newly created page? I'm evaluating potential link partners and seeing alot of this happening and wondering what could be preventing the efficient flow of link juice in these instances
It all depends on the back links and the visits. Even if it's a one clink from a pr5 that does not give it high PR. Again no one knows for real what does Google use to rank Pages.
If you are looking for potential link partners, may be you want to avoid this whole PR game. find people/sites which are in your niche and try to focus on traffic too rather then just on backlink. rhoula has already answered your question
you need inbound links to the subpage to have a high pr. for now, try increasing the priority of the page in your sitemap.
"Newly created" — that's probably the answer. Check for its PR after the next Google toolbar PR export.
No one knows for real what does Google use to rank Pages. People ask how to fake page rank and I tell them how. People still buying fake page rank links, this trick is not new anymore.
It may have zero or less backlinks. Even though it may be a click away, it needs backlinks to get some PageRank.