To those of you that don't think this is a problem:
The debt that the club owes is bad, and will reduce the club's ability to use its financial muscle for transfers etc for several years. What's important about the debt that the Glazers owe separately to the club isn't that it is owed by United, but that United is the most-liquid asset the Glazers have - it's the only thing they own where they can raise cash quickly (by selling players) should they need to.
So while it's not a problem at the moment, it could be a problem should things get worse with the Glazers other companies. Also because it's the only cash-cow in the Glazer empire, it's the last asset they'll sell unless they can make enough on it to clear the rest of their debts and make a profit. So bad news in the other businesses won't force a sale.