Update — On July 7, 2026, Microsoft rolled back the change that caused this issue. A restart of PowerPoint should resolve the issue for any affected users.
A recent Microsoft PowerPoint update has introduced a bug affecting Macabacus users. This is a M365 bug, not a problem with Macabacus — it can be reproduced natively in PowerPoint with no Macabacus add-in involved, and affects any operation that programmatically copies a slide or shape in a read-only presentation.
We have escalated to Microsoft and are awaiting a fix.
What’s Happening
A PowerPoint update recently released by Microsoft introduced a critical bug that throws an error when programmatically copying any slide or shape in a read-only presentation.
Several Macabacus operations work with presentations in read-only mode by design, including library operations involving slides and shapes. Accordingly, affected users will see an error like this when inserting slides and shapes via Macabacus’ Library pane in PowerPoint:
"Slide (unknown member) : Invalid request. Presentation cannot be modified."
Other library content (e.g., images, text) are not affected. Whether your Macabacus libraries are hosted in SharePoint, OneDrive, or in another location does not impact your exposure to this PowerPoint bug.
Affected Versions
Current Channel 2606 is affected (PowerPoint Build 20131.20090, released June 25, 2026). Several Current Channel (Preview) builds are also affected.
The prior release, 2605, is not affected (PowerPoint Build 20026.20182, released June 16, 2026).
To check your build, go to File > Account > About PowerPoint.
What you can do now
For IT administrators, there are two interim options:
Roll back to the prior M365 build. Rolling affected machines back to Current Channel 2605 should restore functionality; we have not been able to reproduce the issue on that build.
Suspend M365 updates. Machines still on 2605 or earlier are unaffected. Pausing or deferring M365 updates keeps them on a known-good build until Microsoft releases a fix.
What we’re doing
We’ve reported this to Microsoft and are pushing for a prompt fix. We also shipped a temporary workaround that restores lost functionality until Microsoft addresses the root cause. Customers whose Macabacus software updates automatically will receive the update soonest (restart required).
For full technical detail, reproduction steps, and ongoing updates, see our Known Issues article.