Root XML Node nwq not found on island - Error Message

A user was modifying a combined analyses with that includes a pivot table. The user added a new alphanumeric field to the analyses. In Step 2 the user was trying to remove some of the existing columns in the pivot table and got this error message.

Can someone explain the meaning of the error message above? How can the user avoid this error in the future?

Here is the user’s account of what happened:

While excluding criteria from a pivot table during Step 2 of modifying a combined analyses, I received this error and was reverted back to Step 1 which was completely blank. I had to click “OK” several times before the error message would go away, but all of the data was still missing and I had to start over. I was utilizing IE 8 with compatibility view checked when this error occurred.