They were using Lehman as their primary broker. Now the accounts have been frozen as administrators sort out the wreckage.
The Reserve Primary Fund money market fund was forced to restate their net value to 97 cents a share to to suspend withdrawals for up to seven days. This after, among other things, they wrote down the value of $785 million of Lehman paper to zero. Yes, zero.
You might want to check what your money market fund is invested in.