The business is no longer able to function due to (usually) large debts and the creditors have foreclosed on loans or similar, but have decided that the company may well be worth more to sell off as a going concern rather than liquidising it's assets......A solicitor specialising in this work is usually appointed to oversee the running of the company until it either pays off it's outstanding debts and becomes solvent again or someone comes forward to buy the company and pay off the debts that way.....If the company is listed on the stock market trading on it's shares has to be suspended also I believe.
Just to add to sft's excellent answer - creditors do not need to be paid off in full. In the recent case of Leeds United many creditors agreed to a payment of about 20 pence in the pound but the Inland Revenue were not one of them!
To expand on Gef's answer, the revenue are a preferential creditor, they always get first dibbs and indeed could get all their money paid to the detriment of the other creditors. The tax man eh, they always get their lump of flesh
As I understand it, the main reason it actually happens is to prevent individual creditors seizing the assets on a first come first served basis. The assets are effectively "secured", pending agreement of all parties on how to re-pay debts.