Login woes: a solution

OK i’ve solved ONE of my problems with the login not working and thought I would share it with you all for future reference.

For background: I was having trouble logging in; You could either not get past the login page (just refreshed only) or not get to the login page at all! Searching the forum showed that many others had the same problem.

I have several wordpress installations, some installed in subdirectories of another. When first installed, you then access the site through this sub-directory url: http://www.originaldomain.com/subdirectory/ and this is the address specified in the General Settings of the wordpress installation. The admin panel is then accessed through http://www.originaldomain.com/subdirectory/wp-admin

BUT… once you point a new domain name that you have reserved specifically for the new WP installation to that location, things slowly start going wrong!

Visiting the site then happens via the new domain url (e.g. http://www.newdomain.com) and that works just fine. While initially, logging in through either http://www.originaldomain.com/subdirectory/wp-admin or http://www.newdomain.com/wp-admin works just fine, slowly this mysterious login problem arises. At first, clearing caches and resetting passwords gets around it, but even that doesnt work eventually.

Its ONLY solved once you reset the wordpress address in your control panel to http://www.newdomain.com directly.

While this may look simple, it tool me absolutely ages to solve.
Hope this helps someone else searching for a solution to the same problem in the future.