Fix: ACRM 15.25.2 Word (VSTO) Office Add-In Installation Fails with Manifest Download/Access Error

Solution

Symptoms (How to recognize the issue)

• Installer aborts with a message such as Fehler bei der Installation. (Installation error).
• The installer reports the manifest could not be downloaded/opened (German wording observed: konnte nicht gedownloadet werden).
• The error references a local file URL similar to:
  • file:///C:/Users/<user>/Downloads/OfficeAddins_15.25.2_full/aurea.office.word.dll.manifest
  • Deployment source may show: file:///C:/Users/<user>/Downloads/OfficeAddins_15.25.2_full/aurea.office.word.vsto

Affected version

• Reported in: ACRM 15.25.2
• Office add-ins package name example: OfficeAddins_15.25.2_full

What’s happening (Root cause)

The Word add-in deployment (.vsto) depends on the corresponding application manifest file:

• aurea.office.word.dll.manifest

If the manifest is missing, blocked, or inaccessible at the path referenced by the deployment, the VSTO/ClickOnce installation cannot continue and the setup aborts.

Common reasons include:

• Incomplete extraction, or installing from the wrong folder.
• Windows has marked the downloaded ZIP as blocked (requires Unblock before extracting).
• Installation started from an unsuitable location (for example, directly under Downloads, a network share/UNC path, or another restricted path).
• Insufficient permissions when launching the installer.

Mitigation steps (Perform in order)

1) Re-extract the Office Add-Ins package to a short local path

1. Create a short local folder, for example: C:\Temp\OfficeAddins_15.25.2\
2. Extract the contents of OfficeAddins_15.25.2_full into that folder.
3. Re-run the installation from the new location (avoid running directly from the Downloads folder).

2) Unblock the downloaded ZIP (if applicable), then extract again

1. In Windows Explorer, right-click the ZIP file and select Properties.
2. If an Unblock checkbox/button is present, enable/select it and apply the change.
3. Extract the ZIP again into C:\Temp\....
4. Retry the installation.

3) Verify required files exist in the extracted folder

In the folder you are installing from, confirm these files are present:

• aurea.office.word.vsto
• aurea.office.word.dll.manifest

If aurea.office.word.dll.manifest is missing:

• Re-download the Office Add-Ins package and extract again (the prior download/extraction is likely incomplete/corrupted, or the wrong package was used).

4) Ensure you are installing from local disk (not network/UNC) and run with admin rights

1. Confirm the install source is on a local drive (for example, under C:\) and not a file share/UNC path such as \\server\share\....
2. Right-click the installer entry point you are using and select Run as administrator.
3. Retry the installation.

If the issue persists

To diagnose the failure deterministically, collect one of the following:

• The exact text shown under the installer’s Details (if available), or
• A screenshot of the directory listing of the extracted add-ins folder (showing whether the .vsto and .dll.manifest files are present and the full path).

Validation (Confirm the fix)

1. Launch the installation again from the re-extracted local folder (for example, C:\Temp\OfficeAddins_15.25.2\).
2. Confirm the Microsoft Office Customization Installer completes without aborting.
3. Verify the Word add-in is installed and available in Microsoft Word (for example, it appears as an enabled add-in—depending on your Office configuration).