1. There's a hidden sheet in your workbook
2. There is a 2nd instance of M$ Excel in the same process running.
Solution for case 1: Unhide the sheet
Solution for case 2: Every new instance of M$ Excel must run in its own process
I hope, it will help to solve the problem.
Jibala
PDF & BCC (Patience Discipline Focus & Belief Confidence Consistency)