[CTPP] Fwd: What to do when steps in Standard Error Calculations return Negative Numbers

Apologies for using this forum but I figured this might be appropriate. I am trying to get the upper and lower bound at the 90% CI around shares of people who live and work in Palm Beach County and who live in PB County but work outside PB county. I am using 1 year ACS data from 2008 and am using table B08007. I am getting a negative number under the square root term and obviously it cannot calculate SE. Anyone has pointers for a workaround or what you did when faced with something like this? I doubt if it can deal with imaginary numbers but if there are any statisticians who can elaborate that would be helpful. I am attaching the actual XLS file and you can see a screenshot of the file here: http://picasaweb.google.com/krisviswanathan/ACS_STANDARD_ERROR TIA, Krishnan -- Krishnan Viswanathan 1101 High Meadow Dr Tallahassee FL 32311