The errors were all within the CalPERS pension fund. The pensions are guaranteed by the state, so the fund is notorious for a complete lack of fiduciary duty, and these types of errors track with the general quality of their operation.

Alternatively, since we're spit balling, the administrators and/or accounting staff decided to strategically error on the side of a shortfall because its politically impossible to get the state to fully fund the pension obligations or to stop effectively raiding it.

Recall that funds like this are one of the largest owners of the hedge funds that drive up property values for American homes via their reckless speculation. The state (well states really -- CA is not alone) desperately needs to make more than market returns to guarantee their unfunded pension liabilities.