How to fix problems with installation of ClickOnce applications

Problem:

You are not able to install a ClickOnce application (e.g. the CodeTwo Exchange Rules Converter) and the following error appears:

Your administrator has blocked this application because it potentially poses a security risk to your computer.
Your security settings do not allow this application to be installed on your computer.

Fig. 1. The error window.

You experience this error even when you try to install the app as an administrator.

Solution:

This problem is related to security options on your Windows machine, not to CodeTwo software. You can experience this issue in various scenarios:

• when the group policy (GPO) in your organization is set to block ClickOnce applications;
• if your organization uses third-party tools, these tools might block the installation of other applications;
• if you have not experienced this issue before, the security settings on your machine might have changed after a recent Windows update.

Usually, the problem does not appear in clean Windows installations and might mean that the security settings on your machine are different from the default Windows configuration.

To solve this problem, you need to:

• add the application's URL to Trusted Sites in Windows,
• check and (if necessary) modify the ClickOnce trust prompt behavior in your environment so that applications from Trusted Sites can be installed on your machine,

or, alternatively,

• deactivate the Internet Explorer’s feature which disables the caching of SSL pages.

​How to add the URL of a ClickOnce application to Trusted Sites in Windows

To fix problems with the installation of the CodeTwo Exchange Rules Converter (which is a ClickOnce app), try updating the URL security zones in Windows: you need to specify that the CodeTwo app comes from a trusted source. You can do that by adding the application's URL to Trusted Sites in the Internet security options:

1. Open Windows Control Panel and go to Internet options (you can also access these settings by opening the Start menu, typing Internet options and pressing Enter).
2. Go to the Security tab and click the Trusted sites zone (Fig. 2., item 1 and 2).
3. Click the Sites button on the right side and add the application's URL, as shown in Fig. 2., item 3 and 4. In the case of the CodeTwo Exchange Rules Converter, the URL is:

   https://install.codetwo.com/CodeTwoExchangeRulesConverter.exe

Fig. 2. Adding the URL of CodeTwo Exchange Rules Converter to Trusted sites.

4. Close the Trusted sites window and click OK to save the changes.

You should now be able to install the CodeTwo Exchange Rules Converter. If the installation window (the ClickOnce trust prompt) does not appear, see section Manage the ClickOnce trust prompt behavior on your machine.

Manage the ClickOnce trust prompt behavior on your machine

The ClickOnce trust prompt is displayed when you install or launch a ClickOnce app. It gives you the option to agree or disagree to install or run the app. Sometimes, the prompt may be disabled for certain URL security zones in Windows. Follow the steps below to check if the ClickOnce trust prompt is enabled for Trusted Sites, and, if necessary, modify these settings.

1. Open Windows Registry Editor (e.g. by clicking the Start button and typing regedit).
2. Find the following key in the registry:

   \HKEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT\.NETFramework\Security\TrustManager\PromptingLevel

3. Find the following entry (value): TrustedSites. If its value is set to Disabled, change it to Enabled. (If the registry key shown in step 2. does not exist, you need to create it first. Then you need to add the TrustedSites subkey as String Value.)

For more information on these settings, see the MS article on configuring ClickOnce Trust Prompt.

How to deactivate the feature for disabling the caching of SSL pages in Internet Explorer

Internet Explorer offers a feature which allows users to disable saving sensitive or private data from the Web to a local disk. It was designed with information protection in mind. While the feature might be useful, it might also prevent the user from installing ClickOnce applications such as the CodeTwo Exchange Rules Converter. Follow the steps below to deactivate the feature and check afterward if it was causing the problem.

1. Open Windows Registry Editor (e.g. by clicking the Start button and typing regedit).
2. Find the following key in the registry:

   [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings]

3. Double-click the DisableCachingOfSSLPages value to display the Edit DWORD (32-bit) Value dialog box.
4. In the Value data: text field, change the value from 1 to 0 and click OK.
5. Close the Registry Editor window.

After completing these steps, try to install your ClickOnce app again.