Overview: Users may sometimes encounter an extension hardening policy error in the Active workpapers Excel taskpane
Error: 'This operation is not allowed due to the extension hardening policy'
Cause
Due to group policy/settings enforcing Extension hardening.
Resolution
Please speak to your IT to disable Extension Hardening Group Policy for your machine.
Option 1: Using Group Policy Editor (for Windows Pro/Education/Enterprise)
Open Group Policy Editor
Press Win + R, type gpedit.msc, and press Enter.
Navigate to Office Policies
For Excel (Microsoft 365), go to:
User Configuration → Administrative Templates → Microsoft Excel → Excel Options → Security → Trust Center
Or, if using the system-wide policy:
Computer Configuration → Administrative Templates → Microsoft Excel → Excel Options → Security → Trust Center
Look for “File Block Settings” or “Security > Extension Hardening”
Microsoft 365 introduced “Extension Hardening” to block certain unsafe file types.
There should be a policy like:
Block opening of unsafe file types
Open Office files from potentially unsafe locations
Disable or Adjust the Policy
Double-click the relevant policy.
Set it to Disabled or Not Configured if you want to allow all extensions.
Click Apply → OK.
Force Update Group Policy
Open Command Prompt as admin and run:
gpupdate /force
Restart Excel to see changes.
Please also see if this group policy can be disabled:
Option 2: Using the Registry (if GP Editor not available)
Open Registry Editor: Win + R → regedit → Enter.
Navigate to Excel’s Trust Center:
HKEY_CURRENT_USER\Software\Policies\Microsoft\office\16.0\excel\security\
OR Alternatively look under KEY_CURRENT_USER\Software\Policies\Microsoft\office\16.0\excel\security\fileblock
(Use 16.0 for Office 2016/2019/365; adjust if older version.)
Look for DWORD values related to extension hardening or blocking, e.g., Extensionhardening, BlockEncryptedFiles, BlockMacrosFromInternet.
Set values to 0 to disable hardening, then restart Excel and test the sheet insertion again.
Option 3a: If Issues persists, you can also try to Add these DWORD values to disable hardening and test which one was causing the issue.
Create the following DWORD values in FileBlock and set them to 0:
DWORD Name | Value | Description |
BlockMacrosFromInternet | 0 | Allow macros from the internet |
BlockEncryptedFiles | 0 | Allow opening encrypted files |
BlockLegacyFileFormats | 0 | Allow legacy file formats (xls, xlt, etc.) |
BlockMac97 | 0 | Allow Excel 97 macro-enabled files |
BlockEmbeddedFiles | 0 | Allow embedded objects in files |
Setting 0 = Disabled / Allow; 1 = Enabled / Block.
Option 3b: In Excel Trust Center (per-user setting)
Open Excel → File → Options → Trust Center → Trust Center Settings → File Block Settings.
Uncheck the file types you want to allow.
Click OK to save.
If the issue persists, try reinstalling the add-in and disable Safe Mode in Excel:
File → Options → Trust Center → Trust Center Settings → ActiveX Settings, then adjust the settings as needed.