This occurs because the Blackbaud NetCommunity page is using a secured HTTPS connection, but some of the content being displayed on the page is referred using the non-secured HTTP URL. This content could be located in Formatted Text or Unformatted Text parts, the page layout, or the site style sheet. 

The browser detects that non-secure content is being included in the secured page and presents a warning to allow the web site visitor to select whether or not to risk displaying this content on the page. Content on the page should be updated to use the HTTPS URL where possible by following these steps:

  1. Edit the part that contains the external content
  2. Change the URL for the external content to a secured connection [e.g. change the URL from "http://exampledomain.tld/content" to "https://exampledomain.tld/content".
  3. Save the change to the part
Warning: Depending on the specific web site that you are obtaining the external content from, that site may or may not be capable of delivering the content via secured connection.  Please contact that web site provider for additional information regarding availability of secured connection URLs for the desired content.

If the mixed content source is not easily detectable, the developer console in the browser can be utilized to find the mixed content referenced on the page. For instructions on how to use the developer console, please review the Google Developers' Guide On Fixing Mixed Content.

For more information about the risks of mixed content on a secured page and how to detect this type of content, please refer to the following browser resources:

Microsoft:
Protecting Consumers from Malicious Mixed Content

Google:
What is Mixed Content?

Mozilla:
Mixed Content Overview

Note: We provide links to third-party websites in an effort to help you resolve your issue. We are not responsible for the information on third-party websites, and we cannot assist with implementing resolutions from these websites.