I hope that someone can shed some light on this for me.
I am running a main site in the root directory, and a test site in a sub-directory.
When I turned on permalinks in the test site, it caused a redirect loop for the main's site login.
Is this common? Could I mistaken in believing that the permalinks in the test site were what caused the redirect loop on the main site login?
To avoid the redirect, I changed link structure on the test site and that worked.