I'd be happy to provide you with that information.
It is a common law rule and is stated as follows:
A corporation has the capacity to bring a lawsuit because it has all the powers of a natural person in carrying out its business. (§ 17; Corp. Code, §§ 105, 207.) However, under a long-standing common law rule of procedure, a corporation, unlike a natural person, cannot represent itself before courts of record in propria persona, nor can it represent itself through a corporate officer, director or other employee who is not an attorney. It must be represented by licensed counsel in proceedings before courts of record. [***5] ( Caressa Camille, Inc. v. Alcoholic Beverage Control Appeals Bd. (2002) 99 Cal.App.4th 1094, 1101-1103 [121 Cal. Rptr. 2d 758] & citations therein.) The same venerable common law rule obtains in federal courts, notwithstanding the comparable federal statute that permits "parties" to plead and conduct their own cases personally. (28 U.S.C. § 1654; [*1146] Rowland v. California Men's Colony, Unit II Men's Advisory Council (1993) 506 U.S. 194, 201-202 [121 L. Ed. 2d 656,XXXXX 716].) The rule exists in most sister states as well, often by statute. (Annot., Propriety and Effect of Corporation's Appearance Pro Se Through Agent Who Is Not Attorney (1992) 8 A.L.R.5th 653 §§ 2, 3, pp. 672, 675.)
CLD Construction, Inc. v. City of San Ramon, 120 Cal. App. 4th 1141, 1145-1146 (Cal. App. 1st Dist. 2004).
Assuming that the DBA that was sued is registered to your corporation,then the plaintiff is not really suing a non-entity. It is suing your corporation, under the DBA. The names of the parties need to be corrected once you have answered. Here is the authority on my answer:
"Use of a fictitious business name does not create a separate legal entity. As an appellate court recently noted, the designation "dba" means "doing business as" but is merely descriptive of the person or corporation who does business under some other name. Doing business under another name does not create an entity distinct from the person operating the business. The business name is XXXXX XXXXX and so too is any implication that the business is a legal entity separate from its owner."
Pinkerton'S, Inc. v. Superior Court, 49 Cal. App. 4th 1342 (Cal. App. 4th Dist. 1996)
But while a corporation may be sued by its fictitious business name, once its true name is XXXXX XXXXX further proceedings should be in the corporate name. Cal. Civ. Proc. Code § 474.
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Please let me know if you need more information or want to discuss this issue further.