I did as you suggested. Using SSH I downloaded the tar ball and decompressed it onto the server.
The first time I tried to log in, which in turn sets up ownCloud, there was an ERROR 500 event and the installation failed.
I deleted the ownCloud folder on the server and unzipped the tar ball again. This time when I tried the initial login I had a server error message similar to the one I first posted, but subsequently I could log in.
I deleted this second install and tried a third time. This time all was well and I was able to log in successfully.
I then tried to upload some files as this was the original cause of the problem. My first attempt at an upload failed with the following message at the top of the web page:
I was then logged out of ownCloud and required to log in again before I could continue.
Finally I was able to upload the 45 test files to the server and delete them successfully, but when I tried to upload the 45 files again, I was once more kicked out to the login prompt.
Trying again, I did manage to upload the files successfully and again delete them.
The total upload size if about 350 mbytes. The method used to select the files was the + at the top of the web page and selecting the 45 files from a folder on my PC.
After the initial yellow error message at the top of the web page, I have not seen it again.
I am not sure at this point where to poin the finger of blame and would appreciate advise.