Legal Question in Business Law in California

Anybody can sue anybody for anything. Your question is whether they can win. The only way you're going to get any meaningful and informed opinion/advice, upon which you can rely with some sense of safety, is to sit down with experienced counsel, who will be able to provide it to you only after reviewing all the facts with you. If serious about getting counsel to do this, feel free to contact me.

Parties to a contract can breach it unintentionally. Your question does not explain what happened, but you seem focused on your lack of knowledge that you were committing a breach -- a fact which does not bar the suit and which will probably not be very helpful in your defense.

Yes, you can be sued, and if you don't defend, you'll lose by default. Better questions would be whether you have a defense, and whether the other party is likely to sue. A party to a contract is generally presumed to have read and understood it, so an inadvertent breach can be the subject of a successful suit by the plaintiff/other party.