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.
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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.

It seems to me that someone used a 30 amp cable to feed two 15 amp circuits. There must be a junction box where the orange cable branches off to two 15 amp cables. You should get an electrician to check it out. You are better off playin' it safe!