In the instructions for showthread.php, you say to find this:
PHP Code:
$postbits .= getpostbit($post);
updateuserforum($thread['forumid']);
eval("dooutput(\"".gettemplate("showpost")."\");");
exit;
And replace it with various stuff. The problem I had with that in my showthread.php, in that whole section of code, on the first line ($postbits .= getpostbit($post)

it had no dot (it was $postbits = getpostbit($post)

.