Hello there!
This error can be generated when there are network connection issues but also when there is a formatting issue with the RSS feed.
We did a quick test in the latest release, and there are no issues with our RSS widgets. We used the below URL to perform the test, so perhaps you also might want to test with this URL to rule out network issues or formatting issues with your URL: http://www.lansweeper.com/blog-rss.aspx
If the above test URL works, but your original RSS feed is still erroring out, we suggest checking if the RSS feed is still valid. You can double-check the URL on this website: https://validator.w3.org/feed/
If these tips don't help, don't hesitate to reach out to support as suggested by @Mercedes_O