What version of UBB.threads are you running? When you run the below MySQL code (CP -> Tools & Information -> Database Tools -> SQL Command) could you copy the output? It sounds like there could be a duplicate entry in the table for one of your groups:
SQL Query
SELECT `GROUP_ID`, `FORUM_ID` FROM `ubbt_FORUM_PERMISSIONS` WHERE `FORUM_ID` LIKE '%New Forum Template%' ORDER BY `GROUP_ID` ASC

You should get a kludge similar to:
Quote
GROUP_ID FORUM_ID
1 New Forum Template
2 New Forum Template
3 New Forum Template
4 New Forum Template
5 New Forum Template
7 New Forum Template
10 New Forum Template
11 New Forum Template
12 New Forum Template

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