Upgrade from vB5.1.5 to 5.1.6 Critical Error - table doesn't exist

[jdj]

I just uploaded the new files to my live site. I upgraded my test site earlier today, that seems to have gone OK.

On the live site now when I try to access mysite.com/core/install/upgrade.php I get the error message Critical Error

We are currently experiencing technical difficulties. Please check back in 24 hours.

I then get emailed an error message saying

Database error in vBulletin 5.1.5:

Invalid SQL:
SELECT * FROM vbnotificationcategory;

MySQL Error : Table 'my_database_name.vbnotificationcategory' doesn't exist
Error Number : 1146
Request Date : Thursday, March 26th 2015 @ 09:24:04 PM
Error Date : Thursday, March 26th 2015 @ 09:24:04 PM
Script : http:///admincp/core/install/upgrade.php
Referrer :
IP Address : my IP address
Username : My_admin_user_name
Classname : vB_Database_MySQLi
MySQL Version : 5.5.38

I've tried uploading the files again. It doesn't make any difference, I get the same error message.

My site is now down and I can't turn it back on again. What do I do to retrieve it? I've put in a support ticket but just in case anybody has any ideas I'm posting here.

[jdj]

No idea why this happened but for the benefit of anybody else who sees a similar problem I changed the two config files to debug mode then uploaded them. Then I was able to access the upgrade script.

I have no idea why this worked.