From time to time, a weird formula appears in a cell in an old worksheet without my entering it when I first open its workbook. When that happens, I cannot enter data anywhere in the worksheet until I delete the formula. In the past, the formula has triggered a circular reference error message. Today, a formula appeared but did not generate an error message. I could not delete the formula or enter data anywhere. After closing the blank workbook which opened when I first opened Excel to access the old workbook, I was able to enter data in the old worksheet and delete the weird formula. What is causing this problem?
