FB08 Error Do not assign any objects in cost accounting to account

One of our users was reversing an accrual entry today. When she tried to do the reversal, she got the warning message "Do not assign any objects in cost accounting to account XXXXXX" She does this reversal to this very same GL account every month.

No changes have been made in configuration or to the GL account. She created the journal entries that are being reversed in the same manner she always has. What would cause this warning to suddenly appear?

I realize I can suppress it, and I may have to do that next month, but I'd very much like to understand what changed in our system to cause this error to appear.

We ran a reversal for a similar entry in our Q system and it worked just fine, no warnings at all.

Thanks much for any insight.

Andrea