"Open link" command fails

Web site link must specify protocol

All your web site links assigned to Link field must begin with http:// or https:// protocol (only secure sites support https, so use what your web browser shows for specific site). That way Password Agent knows that these are web site links, because Link field can also contain path to executable program which can be opened with Open link command as well.

Valid web site links:

http://www.moonsoftware.com or https://www.moonsoftware.com

Not valid web site links:

www.moonsoftware.com or moonsoftware.com

Protocol is present but “Open link” still fails

If you have links in the proper format, then the problem likely is that you have no default web browser properly set. See How to set default browser.