OK... been a long time, but I found the log files in \cache\, and find this error:

[14-Aug-2012 16:48:48] PHP Warning: Cannot modify header information - headers already sent by (output started at /home/my_host_site/public_html/includes/languages/english/create_account_success.php:18) in /home/my_host_site/public_html/includes/functions/functions_general.php on line 45

I'm now looking at the document that might have my answer... blank line at beginning of file... not sure which one, but I'll check both.