The 2007-2008 financial crises has made it painfully obvious that markets may quickly turn illiquid. Moreover, recent experience has shown that distress and lack of active trading can jump around between seemingly unconnected parts of the financial system contributing to transforming isolated shocks into systemic panic attacks. We develop a simple two-period model populated by both standard expected utility maximizers and by ambiguity-averse investors that trade in the market for a risky asset. We show that, provided there is a sufficient amount of ambiguity, market breakdowns where large portions of traders withdraw from trading are endogeneous and may be triggered by modest re-assessments of the range of possible scenarios on the performance of individual securities. Risk premia (spreads) increase with the proportion of traders in the market who are averse to ambiguity. When we analyze the effect of policy actions, we find that when a market has fallen into a state of impaired liquidity, bringing the market back to orderly functioning through a reduction in the amount of perceived ambiguity may cause further reductions in equilibrium prices. Finally, our model provides stark indications against the idea that policy-makers may be able to inflate their way out of a financial crisis.