[Opserty]

Questions/Problems regarding custom modifications/styles should be asked in the thread, site or board from which you downloaded it, as they are in the best position to help you.

Reading through the modification's thread it indicates that it is only supported on the third-party site. You may wish to post there in order to receive a response.

If you need to revert and out of date templates then you will need to do so (bearing in mind any modifications to them will be lost). The problem is most likely caused by a missing security token field in the form, you could try locating the forum and fixing it yourself. See the "Template Changes" section of this thread for the code to add.

It seems odd the style was released for 3.7 and is still encountering this error, it must have been overlooked by the author.