You might need to use another browser (if using MS Edge) and if the site requires HTTPS check, you might have to disable that in your anti-virus program for the time being.
If you are referring to the Message+ application, I too am having issues in Windows 10. The application itself works, but now all pictures that are in MMS do not display and instead show as being "Invalid image format or image deleted", which did not happen under Windows 8.1. Not sure what the issue is at the moment but I suspect something changed in how Windows 10 displays images. Note that this is the application, not the website, so any references to Microsoft Edge (browser) do not apply.
I am hoping for an update to the Message+ application, but not holding my breath as it doesn't seem to get updated often at all, and there are still crashes in the console that I can read which happen if I leave Message+ running on my computer for long periods of time.
If I may make a suggestion:
You can use Mighty Text app for free on your phone. It works with Verizon Messages, stock messengers and such. It gives you the ability to display contact pictures and create and respond via webpage and via pop up windows. You can also backup messages if need be, but by default I believe 90 days are saved regardless. I have been using it for years on many phones and PCs, including the Win 10 I am on now.
It runs in the background like the VM+ service/process on the phone and you don't actually interact with the phone side app. You might prefer the interface of VM+ on the PC via desktop app or webpage option, but this works the same way and might be a viable alternative until VM+ is updated for Win 10.
Thanks for the suggestion. I was able to uninstall Message+, then reinstall it and the images are now appearing as they should. It's an odd situation, considering my Windows 10 install was done as a clean install and not an upgrade in place. Either some app that was installed after Message+ caused a corruption of some file(s) in Message+, or something else odd took place, but it appears the reinstall corrected the issue.