Line fault at the outlet -- do I need an electrician?

Yesterday, I got a Panamax, Max 1500 surge protector and line conditioner. (I got a very good deal on it, and am just trying it out.)

I plugged it into an outlet I've been using for a while and one of the red lights on the front lit up saying "line fault." (I'm not sure how this is different from a "ground fault." Maybe it's the same.) The Panamax does not do this with other outlets in the room. They seem ok.

So, I know this means that the outlet is improperly wired. My question is, might this be a simple thing to check and/or fix? Any suggestions most appreciated. It's the only outlet I can use to have my audio set up where I usually have it. Now is not an optimal time to call an electrician. If this is a big problem, I'll try out my gear somewhere else in the room, but if I can fix this without too much expertise, that would be ideal.
8700e65e 845e 4b1b 91cc df27687f9454hilde45
Orange romex is 10 gauge 30 amp cable. I doubt that it  was used for just 15 amp room outlets. You will have to find where the hot and neutral are wired reversed! If you throw the breaker off at the main panel are you sure that that circuit only controls those outlets? You might find that it is feeding other outlets in your house!
Wait a minute the subpanel only has 1 thick orange wire coming out ? You sure that's not going in? Is the subpanel next to a main panel connected with conduit? If there's more than 1 breaker in the box must be more than one wire going out unless they split that large wire and put 2 breakers on it and shared a neutral. If they did must be a junction box somewhere where they split up. If there is only 1 wire going out and more than 1 breaker in that subpanel call an electrician to trace down this mess.
TBC: A subpanel is a panel downstream from another panel. Meaning, there’s a panel before it that has a fuse/breaker that can turn off the power to the sub panel.  There is one set of breakers/fuses to a subpanel, but the subpanel may contain any number of breakers.

This is useful since you can disconnect the power to the entire panel before opening it.
Maybe the terminology is messing me up.

I have one panel in the house.

At the top, is the master on/off. Below are the breakers. I thought that's what you meant by subpanel. It is not a separate panel, in the sense that it is not another separate metal rectangle. There is one metal rectangle.

The subpanel contains, maybe, 30 breakers.
I followed a bunch of wires out of the box (9, 10?) and the orange one split off to the side of the house where I presume it is feeding the circuits/branch I mentioned.