Camera Raw Plug In

According to the Help page at Adobe, the D3400 requires ACR 9.7 and the A7 III requires ACR 10.3:

Cameras supported by Camera Raw

According to another Help page at Adobe, ACR 9.7 is only compatible with PSE 15 and newer and the page has not been updated to the newer PSE16/2018, yet, for whatever reason:

Camera Raw plug-in and Adobe application compatibility

So the D3400 is supported by a payfor upgrade to PSE16/2018--you can download and run the trial and see that it works before paying anything:

Easy Photo & Video Editing Software | Adobe Elements Family

The A7 III can also work with a payfor upgrade to PSE16/2018, although PSE2018 it currently ships with ACR 9.12 and can only be updated to ACR 10.2 at the moment, despite an Adobe Support employee has replied to a forum post I've seen, saying that PSE 2018 will eventually be updated to use ACR 10.3 and support the A7 III natively; however, it doesn't currently and maybe the support person is mistaken. 

I am running Windows 10 64-bit and have been able to successfully hack my PSE 2018 to open A7 III raw images, by installing the Photoshop CC 10.3 plug-in and copying it over to where the PSE 2018 plug-in needs to be.   This is all on 64-bit Windows 10.  Here is a forum post where I describe how to do the copy as well as a subsequent reply including comments from a Support chat:

https://forums.adobe.com/message/10316185#10327630

Note that the user I was replying to initially couldn't get it to work, but upon my urging, tried it again, and things worked ok for her.

Alternatively to the payfor upgrade and possible hack of PSE2018, you can also download and install the *FREE* DNG Converter 10.3 or newer, and use it to convert A FOLDER of native raw files for your camera to DNGs, and those DNGs but not the native raw files, will open in older Camera Raw (ACR) plug-ins.  The free but extra-step-cumbersome DNG Converter can be found on the Adobe Updates page:

Adobe software and product updates

I'm guessing the error message actually says the Raw files from your camera are not recognised by your version of Camera Raw.

Which camera make and model are you trying to import Raw images from?

Elements 14 ships with Camera Raw 9.0 and can only be updated to Camera Raw 9.5.

Your camera probably requires a newer version of Camera Raw which is only compatible with later versions of Elements. There are workarounds if you tell us which camera you have.