Update with additional information

Since I started this thread i have found out the following:

1. I cannot right click and delete any folders in the folder tree. 'Delete' is greyed out. I can delete all the folders with 'Empty Deleted Items Folder'

2. This one is probably important. I backed up my IMAP .ost file and then renamed it so Outlook would recreate a new .ost file. When it recreated the new .ost file the same folder tree appeared. I logged on to my webmail and there is no evidence of the folder tree.

Now, when I open Outlook, there are three other .pst data files opened as well. I guess it is time to close them and see the effect on this folder tree ???