Tried to add a new ship, got an error I've never seen.

You set something to a bad value. Sins doesn't like it. Given its fighters, you probably gave it an ability or messed with its speed/turn rates.

Erm. So what do I do to fix it? I mean, does it give a clue?

I went to give the fighters each two weapons- is -that- it?

Okay, no. So, that did nothing; I set all the values to default- in fact I loaded the bomber template for each of my new strike craft. And it still gives me the error of doom.

Nope, typically it means the game ran into a value that it doesn't know how to handle. Keep in mind fighters are a very rigid entity type, they have lots of other restrictions that other types don't have. Experimenting with them will get you a lot of errors like this, so don't proceed unless modding it is worth losing a weekends worth of sanity at least.

The roll rate and different vectors they have (speed settings in all directions) aren't completely variable.

The best thing to do is look at the vanilla ships and strike craft and the ones in other mods--like Distant Stars for "safe" settings.

I'm not looking at files right now but it's more the strafe and roll values that are super picky.  Line of flight acceleration, deceleration and max speed are more tolerant.

Okay, no. So, that did nothing; I set all the values to default- in fact I loaded the bomber template for each of my new strike craft. And it still gives me the error of doom.