This is probably a mixed content error. You might want to look at other cases on this forum where people have had trouble with this issue:
This problem can arise when you include content such as scripts, images, or stylesheets via HTTP URLs inside a page which is itself loaded over HTTPS.
I agree with @rg305 that we’re really here more to help out with Let’s Encrypt certificates rather than with Network Solutions certificates, but please consider our free certificates in the future if you’re the system administrator of your site or ask your sysadmin or hosting provider to consider them if you aren’t. (If you’re happy paying Network Solutions for your certificates, that’s fine too—but as @rg305 pointed out, they also have their own support channels.)
Edit: there are also general web development and system administration forums where questions about any kind of certificate error would be on-topic regardless of where the certificate is from. A lot of people here suggest Server Fault https://serverfault.com/ for the system administration side; I don’t happen to know an equivalent for web dev stuff, but I’m sure it’s out there somewhere!