that is the generic message.
do you have the server logs turned on in the the ubb control panel.
you can view the actual error there.
If not then you can edit a file to display the actual message in the browser.
you also should not leave it enabled because any user will see the info which can cause a security risk. You should enable the server logs in the ubb control panel.
anyway edit
libs\mysql.inc.php
find
// IF YOU SET THE VARIABLE BELOW TO 1 IT WILL SHOW THE SQL ERRORS TO ALL
// USERS. USEFUL IF YOU CANNOT LOG IN AND NEED TO SEE THE SQL ERRORS
$showerror = 0;
set it to
$showerror = 1;
go back and view the forum in the browser.