It seems that upgrading is fraught with danger :(
I write this post in the hope it may trigger some ideas that may help resolve the issue.
I have tried upgrading another site (from 4.0.3 to 4.3.5) which produced errors on the following SQL Provider updates:
3.2.3
3.3.1
4.3.1
In ordere to get these to run I deleted the content of the Folders and Files tables and ran the script manually.
I had assumed file syncronisation would re-populate these tables but this failed. I then found that I could not read the event log. A solution to the event log problem was found at
http://support.dotnetnuke.com/issue/ViewIssue.aspx?ID=4273.
Further investigation lead me to import the deleted content of the Files and Folders tables. Sync still failed and File Manager in Admin and Host also produced an error. I then began comparing the folder structure on disk with that listed in the Folders table. I found quite a lot of folders listed in the Folders table that in fact did not exist on disk. These were mainly skin and container folders for the t-worx, XD and Salaro skins originally released with early versions of DNN.
I brought the Folders table in line with the structure on disk. I could then see the folders listed in File Manager. However they all looked like parent folders. I then added "\" to the end of the folder names in the Folders table. File Manager then listed the folder structure correctly and the Syncronisation task runs successfully.
I still have one problem to solve:
How do I get files to list in FIle Manager? The folder structure looks fine but no files are shown in any folder! The Files table is empty. WHat does Syncronisation actually do? Does it not populate the Files table? Will I have to populate this table manually?