Explanations for the global financial and economic meltdowns generally focused on a few particulars. For the right, poor people caused the crisis through reckless borrowing, while the subsequent deficit was made worse by reckless spending on the poor. Worse than the poor themselves are the socialistic legislators who introduce ridiculous laws forcing companies to cease practises such as 'red-lining'. For the centre-left, the power of a barely regulated financial sector allowed the banks to make irresponsible decisions, and speculators to wreak havoc with economic stability by blowing bubbles then bursting them and making off with the dough. Though more sociologically realistic than its rightist competitors, this account neglects the reason for the financial turn in the first place, which was the otherwise intractable crisis of capitalist profitability.
The underlying problem is the impossibility of rational economic calculation in a capitalist system. Decisions have to be made by competing private firms which consistently misrepresent themselves to one another, to their workers, to their creditors, and to their consumers. As we usually discover in the middle of a crisis, misrepresenting one's assets and rate of return is normal practise for a capitalist entity. Not only that, but they consistently undermine any basis for predictability, and thus for rational calculation by revising the terms of their production, by downsizing, by cutting wages, tossing aside worker-management agreements, etc. etc. The only mechanism for calculation within the sphere of private accumulation is competitive market pricing. To see this as a secure basis for economic calculation, one has to also accept a number of philosophical and normative commitments that are quite eccentric: extreme methodological individualism, subjective value theory, the Kantian epistemology of the Austrian school, etc. These are not ideas one subscribes to lightly, or without a delight in perversity.
In fact, market pricing can tell us a thing or two. It can tell us something about the range of options available to us, with our cash, as private consumers or entrepreneurs. It can tell you what each purchase or investment will cost you. About the social effects of market transactions, however, it can't tell us a thing. This is no small matter. A system that persistently closes off fields of information to us, disclosing only that which pertains to our individual aggrandisement, is one that rewards behaviour that, while beneficial to the individual capitalist or consumer, is socially destructive and irrational for the economy as a whole. As to the information relevant to investment decisions, market pricing discloses surprisingly little. Suppose you are a capitalist. What will be rational to invest in tomorrow depends on what other capitalists are planning today. But whether what they are planning will work depends on what you are planning. And being capitalists, you don't share information around willy-nilly. It isn't the done thing. More to the point, you would need some sort of aggregate information about projected social needs, long-term developments, demographic changes, etc. Market pricing will tell you something about what was in demand yesterday, but it can't tell you what will be in demand thirty years from now.
So much the worse if you aren't a capitalist. If you're a capitalist, your only problem is how to improve returns on investment, usually in the short-term. Beyond that predatory social role, a whole series of problems enter one's vista. The question of how to rationally allocate investment, and structure social consumption in a rational manner, involves prioritising needs and wants in a way that requires information that market prices don't provide. Do you build social housing, raise incomes, or invest in a new marina? If you're a capitalist, it's easy - the marina offers more returns, hence more money for future investment and accumulation. If you're not a capitalist, other considerations hove into view. Or take pensions: how much of the social product should be set aside for future consumption? Should this be a fixed amount, or does justice demand that it increases as social production increases in the future? And what sort of infrastructure and public goods will future generations need? What about 'green' development? The only way market prices will help anyone make such decisions is by alerting investors and consumers as to what such decisions will cost them in the immediate term - hence, the attempt to meet such challenges through engineering market-driven, financialised measures such as carbon trading, pensions linked to the stock markets, etc.
In the real world, rational economic decision making is only possible to a limited extent due to the existence of an extensive non-market sphere, socialised public bureaucracies, national statistics agencies, offices for public planning and development, local authorities with oversight, etc etc. Tellingly, their behaviour becomes more irrational, wasteful and incompetent the more they are penetrated by marketised logic, the more they attempt to behave like corporations. They accumulate high overhead costs, duplicate capacity, fail to collect relevant information, and undermine the very rationalising aspects of service delivery that they are there to provide.
The core of the capitalist calculation problem is this: as a system of competitive accumulation, it involves individual capitalists in attempting to extract surplus value from the unique commodity known as labour-power; but to realise that surplus value, they must be able to occupy more of the market than their competitors, and engage in labour-saving innovation and rationalisation; but while this may be rational for individual investors on the basis of current market prices, in the aggregate it results in less labour-power being employed across the industry, thus a reduction in the total surplus value produced*; so while individual capitalists can increase their share of total surplus value, the aggregate tendency will be for the rate of return on investment to decrease, thus for investment itself to decrease, and in the long run for capitalism to enter into repeated crises and contractions. Irrational and anarchic, crisis-prone, with no means of rational planning and prediction, and ultimately bailed out by governments who socialise its losses, capitalism has one hell of a calculation problem.
Meanwhile, I hear tell there's a socialist calculation problem...?
*Update. Rick Kuhn points out that there is a mistake here: "This says that there is a fall in the absolute amount of labour-power employed and sv produced. In fact the organic composition of capital can (and often does) rise as the employment of labour power expands and the absolute mass of surplus value created rises. The issue is that new investment is more capital intensive so there is less labour power (and, given a constant rate of exploitation, surplus value) relative to total capitalist outlays on labour power and constant capital. The decline in the rate of profit may choke off investment before a decline in employment which is then a consequence of the crisis. Conversely, boom phases during which there is both rapid investment can be accompanied by both falls in the organic composition of capital and rises in employment."