Ever tried to log on in Test and Production at the same time, especially under Windows 8?
Easy if you open two (or more) independent Excel session, be either:
1) RUN –> EXCEL /X
2) click ALT on your key board and hold it and than right-mouse-click on the excel-icon in your task bar.
Than you can log on into a different IBP system, or just have your big non-IBP-excel-file in a different session, so if one of them crashes the other still remains.