Knowledge base KB0237

Conflict with Microsoft Azure Information Protection add-in: Subclassing error in PowerPoint and Excel


When I close PowerPoint or Excel, I receive the following error message:
CRITICALWITHMSG library\ui\win\safesubclassimpl.cpp(392): APIERR 1400 Invalid window handle.

When multiple PowerPoint (or Excel) files are open and the Microsoft Azure Information Protection (AIP) bar is shown below the ribbon, this error may occur when closing the last PowerPoint (or Excel) file. However, other add-ins must be present as well. The issue is reliably reproducible, e.g. when Capital IQ is enabled. For detailed reproduction steps, please click on:

Reproduction with think-cell, Microsoft AIP and Capital IQ:

  1. Open new blank PowerPoint [or Excel] file
  2. Open second new blank PowerPoint [or Excel] file, e.g., with CTRL+N
  3. Make sure the Microsoft AIP bar is shown below the ribbon: Home > Sensitivity> tick Show Bar
  4. Go to S&P Capital IQ tab
  5. Charting > Charting > Launch Chart Builder
  6. Close 2nd file > Don't Save
  7. Close 1st file > Don't Save
    > CRITICALWITHMSG library\ui\win\safesubclassimpl.cpp(390): APIERR 1400 Invalid window handle.


Such errors in think-cell are caused by a programming error in another add-in. Our developers analyzed the issue in detail. In this case the issue is caused by the Microsoft Azure Information Protection (AIP) add-in. According to our analysis, hooking/unhooking issues cause this problem when multiple add-ins are available.

A hook is a mechanism by which a function can intercept events before they reach an application. The function can act on events and, in some cases, modify or discard them. For further details, please see KB0201.

Other add-ins known to cause such issues are listed in KB0169.


We received the feedback from Microsoft that the AIP client is in maintenance mode. Microsoft does not recommend using the AIP add-in for Office, because, i.e., "Add-ins are less stable because they can conflict with other add-ins that can result in Office apps hanging, crashing, or automatically disabling the add-in." Instead, Microsoft recommends using the Microsoft Information Protection (MIP) built-in labeling for Office apps.


The problem seems to disappear when turning off the Microsoft AIP bar below the ribbon in PowerPoint and Excel. To turn it off, go to Home > Sensitivity > untick Show bar. In any case, please ask your internal IT for advice.

Contact support

In case you are still experiencing issues without the Microsoft AIP add-in, proceed as follows:

Please send us the think-cell log files. For this, open PowerPoint or Excel and go to Insertthink-cellTools Tools Menu icon. Request Support. The log files will be automatically attached to a new email.

If neither works, you can find the log files as explained below:

  • Open a new Windows Explorer window, type


    into the address field, and press Enter

  • Please send all files with the extension .log contained in this folder to our support team.

    This may be any of the following files: POWERPNT_log.log, EXCEL_log.log, TCMAIL_log.log, TCUPDATE_log.log, TCRUNXL_log.log, TCASR_log.log, PPTTC_log.log, setup_think-cell_xxxxx_log.log.

  • If you want to browse to the directory:

    The full default filepath is C:\Users\[USERNAME]\AppData\Local\think-cell. If you cannot find this, it is probably set to invisible. You can change that in Windows Explorer by checking:

    • Windows 7:
      OrganizeFolder and search optionsViewShow hidden files and folders.
    • Windows 8, Windows 8.1 and Windows 10:
      ViewShow/hideHidden Items.

    In addition, if think-cell is active, please click on Tools Tools Menu icon. About in the think-cell toolbar and send us a screenshot of the think-cell info window.