When This Error Occurs

You'll see this error message during the ClickOnce download process, before the client application launches:



It indicates the ClickOnce installation itself has failed.

Initial Troubleshooting Steps

To identify the specific cause, click the Details button when the error appears. This opens a Notepad window displaying the complete error message, including an ERROR SUMMARY section that contains diagnostic information.

Diagnosis and Solutions

Step 1: Verify the Application URL

Locate the line beginning with "Exception reading manifest from […]" and check the URL that follows.

If the URL points to a different server (such as login.microsoftonline.com instead of your application server), this indicates a connection interruption. For example, if Azure presents a login prompt before the client can reach the application server, ClickOnce cannot proceed and will fail.

Solution: Configure network access so the client computer connects directly to the application server without intermediate authentication steps.

Step 2: Check for Manifest File Issues

If the URL correctly points to vision.application on the application server, examine the error message that appears immediately below.

Error messages indicating file corruption:

• "DTD is prohibited in this XML document"
• "Data at the root level is invalid. Line 1, position 1"

These messages suggest the vision.application file is either corrupted or not being read correctly.

Solution: Verify that vision.application is a valid manifest file by comparing it against a known working backup, or rebuild the ClickOnce package.

Step 3: Resolve Duplicate DLL Errors

If you see the error "Exception from HRESULT: 0x80070C81", this means the ClickOnce package contains duplicate DLL files. This typically happens when the Excel Importer has been added to the client package in a subfolder.

Solution: Ensure the ClickOnce package includes only the application client without any additional Pentana.Tng DLL files.