One of my users reported issues with an Excel document when removing subtotals. The client is using Office 2010 x86 and I am using Office 2010 x64. I let the process run for nearly 6 hours and it still hadn't finished.
I have also attempted this with Excel running in safe mode to disable any addons that might be slowing it down. I also checked CPU affinity to make sure all cpu cores were available. I did notice in task manager that Excel never uses more than 25% of the cpu.
Here are the steps that I am taking: http://office.microsoft.com/en-us/excel-help/remove-subtotals-HP010079193.aspx
Is there a solution to speed this process up?