Since you move the profile, I suppose you know that for Windows 2000/Windows XP that the profiles and mail are in the following path:
C:\Documents and Settings\user_name\ApplicationData\Mozilla\Profiles \profilename\xxxxxxxx.slt\Mail
NOTE: These files are hidden by default.
To see hidden files:
1. On the Tools menu in Windows Explorer, click Folder Options
2. Click the View tab
3. Under Hidden files and folders, click Show hidden files and folders
If you have a single profile, it may be trickier, but, since I have more than one, it is no problem, because I can select the desired one from the profile manager. Did you remove 1.4 before installing 1.6?
The biggest problem may be in your attempt to move. Never,ever move. (how did you move, by the way, and from where to where?) Always Copy and then Paste. By doing this you cover yourself from possible mistakes.
If you had not attempted to move, it would have been no problem, but if you did and don't know how you did it, the only possible work around, would be to create a profile for 1.6, and enter exactly the same name which you had before, and it should be in the correct folder.
UserAgent: Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.4) Gecko/20030624 Netscape/7.1 (ax) (CK-SillyDog)