Update : Jan. 04, 2010
As explained in 'What are the 'daily price limits'?', all stocks have fixed ranges within which their prices can fluctuate during a day. Occasionally, as mentioned in 'Why are special quotes sometimes not renewed to their daily limit prices? ', a special quote may be continue to be renewed until it reaches this daily price limit. As a result of strong negative or positive public sentiment, there may be occasions when there is a major order imbalance at either end of these daily price limit parameters.
If TSE ignores these situations and does nothing to rectify the situation at the closing auction investors will be deprived of the opportunity to trade these stocks. So TSE uses a special mechanism to determine the afternoon session closing price when the last transaction took place at the limit price, and the normal Itayose method cannot achieve execution for the closing price.
When there are insufficient shares to meet these requirements, trading will close without a closing executed price. (For a detailed methodology please see 'How are closing auctions at the limit price processed? (Part 1)'.)