Congratulations on a successful upgrade to Netscape 7.2... Sorry the "send later" function still isn't working when you modify the Unsent Messages folder location.
Can you use "send later" without errors if the mail.default_sendlater_uri preference is reset to the default Local Folders location?
If the problem only occurs when you attempt to switch the active Unsent Messages folder to a specific mail account, I would reset the preference back to the default "Local Folders". Next, I would try removing and then recreating the problem mail account, using the "Remove Account" and "Add Account" buttons in the main "Mail&Newsgroup Account Settings" window.
This will add new entries in the prefs.js file and create a new, empty "pop-server.midsouth.rr.com" folder in your ...\Mozilla\Profiles\"profilename"\xxxxxxxx.SLT\MAIL folder, named something like, pop-server.midsouth.-1.com , in addition to the current "pop-server.midsouth.rr.com" folder that now holds the Inbox, Sent, and other mailbox files... So, if you have current mail, you could EITHER copy the current mailbox contents within Netscape to Local Folders before removing and recreating the mail account ....
OR, after recreating the mail account you can simply use the Mail&Newsgroup Account Settings, Server Settings, "Browse" button to the right of the
Local Directory field, to point back to the original MAIL\ pop-server.midsouth.rr.com folder ..... details here:
http://home.att.net/~cherokee67/ns7lostprofwinxp.html
If you prefer, create a new profile and then migrate your old MAIL and other profile data to the new profile if the "send later" feature works in a new profile, using one of these pages as a guide for migrating specific data like Mail, address book, passwords, bookmarks, etc:
http://ilias.ca/netscape/profilefaq/#transferring (under "Selectively Transferring certain data")
http://home.att.net/~cherokee67/NS7newprofile.html
http://users.adelphia.net/~irwingreenwa ... ml#copying
Then modify the mail.default_sendlater_uri preference again, once the new account or new profile is set up.
Hopefully, someone else might come up with an easier fix.... but, If I were you, I would simply use the default "Local Folders" Unsent Messages folder if it's working OK.
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.5) Gecko/20041217