Assuming your system is even remotely similar to mine (I used the ABC Company data), try this:
Make sure Excel is closed.
Run the report from the Report Manager Menu.
When the mapping tool first pops up, click Cancel.
When the Excel spreadsheet comes up, right click the Notes tab and click unhide.
Unhide Sheet1.
Check the list of codes in the AccountGroup and AccountGroupDesc columns. Should be columns BO and BP.
--OR--
Use Find in Excel to search for the bogus codes but be sure to do a case sensitive search.
See if the bogus codes are listed there, somewhere in those columns or located in the search.
If those columns have the bogus codes, then I'm wondering if the container is set up incorrectly.