obviously the error is in newthread.php so like SmEdD recheck your edits.Cant blame the store hack - user error is the problem here as the store hacks installs fine.
Failing you cant suzz it just re-upload newthread.php and then do it the edits for that file again.
Do same for newreply.php as well
/me shouts :`you did backup files before you edited em did`nt you?`
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