I've just upgraded from the Demo system to V5.4.1.
When I go to a Board from my Main Page (ref: http://www.forums.pctechguide.com/w3t/wwwthreads.php?) I get the following error message:
SQL ERROR: Unable to do_query: SELECT U_Username, U_Password, U_Display, U_Groups, U_Sort, U_View, U_PostsPer, U_TempRead, U_FlatPosts, U_TimeOffset,U_ActiveThread, U_StyleSheet, U_Status, U_Privates, U_FrontPage FROM w3t_Users WHERE U_Username = 'daveande' AND U_Password = 'rsq76Hdo8WSWQ'

Unknown column 'U_ActiveThread' in 'field list': 1054

Warning: Supplied argument is not a valid MySQL result resource in /virtual/w02-0016/w3t/mysql.inc.php on line 71

Warning: Cannot add header information - headers already sent by (output started at /virtual/w02-0016/w3t/config.inc.php:249) in /virtual/w02-0016/w3t/postlist.php on line 312
Since no-one else appears to be reporting a similar problem, I suspect that this may be to do with problems I had in converting my Demo database to the V5.4 format. After a couple of prior failures to get <altertable-demo-5.4.php> to run - finger trouble on my part! - when it did finally run it gave me the following error messages:
Altering the posts table to better designate main topic posts (Speed improvement)...

Re-indexing the main topics for each board...

Altering Users table to allow for thread age display preference...

SQL ERROR: Unable to do_query: ALTER TABLE w3t_Users ADD U_ActiveThread INT(4) UNSIGNED ADD U_StartPage varchar(2) DEFAULT 'cp', ADD U_Favorites varchar(250) DEFAULT '-'

You have an error in your SQL syntax near 'ADD U_StartPage varchar(2) DEFAULT 'cp', ADD U_Favorites varchar(250) DE' at line 4: 1064Creating the table to store favorites and reminders...

Creating the table to store posts that a moderator has been notified on...

Done...
What's my best course of action from here? If necessary I'm happy to scrap the existing Boards and start over from scratch. Can I do this simply by running <createtable.php>? Do I have to do anything prior to this to get rid of the existing database? I guess I'll then be at the point where the first Registered User gets full Admin powers?
Thanks in anticipation.

Looks like there was a slight problem with the altertable script. You should be able to fix that by doing the following command from the mysql prompt or from the database manager in the admin section if you can get in:

ALTER TABLE w3t_Users
ADD U_ActiveThread INT(4),
ADD U_StartPage varchar(2) DEFAULT 'cp',
ADD U_Favorites varchar(250) DEFAULT '-'

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Scream
<A target="_blank" HREF=http://www.wwwthreads.com>WWWThreads</A>

Thanks Scream
That had some effect - but it doesn't appear to have completely cured the problem.
Now, when clicking on a Board from the Main Page

(http://www.forums.pctechguide.com/w3t/wwwthreads.php), the error message I get reads:
Warning: Cannot add header information - headers already sent by (output started at /virtual/w02-0016/w3t/config.inc.php:249) in /virtual/w02-0016/w3t/postlist.php on line 312
Also, something that looks as though it may be a related problem. When I try to use the Jump To box to go from one Board to another, I get the following:
Warning: Cannot add header information - headers already sent by (output started at /virtual/w02-0016/w3t/config.inc.php:249) in /virtual/w02-0016/w3t/jumper.php on line 24

This means you have a space or blank at the very end of your config.inc.php file after the closing php tag. PHP treats this as header info and will give this error.

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Scream
<A target="_blank" HREF=http://www.wwwthreads.com>WWWThreads</A>

Thanks Scream - that does it!
Guess I'm not the first user you've had to put right on this particular matter!?!