Formed a ca llc but never conducted any business,

California law imposes a minimum franchise tax each year on any corporation or LLC. Even if the LLC does no business has no assets, the LLC owes the tax.

However you personally probably do not owe the tax. The Franchise Tax Board will keep sending you assessment notices - perhaps even for years. But it is very unlikely that you, personally, owe the money.

You may not want to formally dissolve the LLC. To do that you will be required to pay all back taxes. In addition, you personally will be required to sign a personal guarantee for payment of the LLC's taxes. If you do that, you personally could be required to pay.

What is this annual registration fee you refer to? And why would an individual and not the LLC alone be responsible for it?

That may vary by state. In California there is an annual $800 minimum tax on LLC's and corporations. But it normally owed by the LLC, not the individual who set up the LLC.

Isn't there a CA Secty of State registration fee? It's $20 per year for corporations, as I recall, I thought LLC's had the same requirement. Not sure who is liable, but it's not big dollars in any case. I don't know offhand what steps are taken by the state to collect this for de facto out of business entities.

In CA there's a requirement that the officers of a corporation and LLC be identified at least every two years, and there's a $25 fee for filing that document. I'm not aware of any other regular fee other than the $800 minimum tax.

Isn't there a CA Secty of State registration fee? It's $20 per year for corporations, as I recall, I thought LLC's had the same requirement. Not sure who is liable, but it's not big dollars in any case. I don't know offhand what steps are taken by the state to collect this for de facto out of business entities. ========== Try $800/year. Similarly, in Nevada: An LLC and Corporation have the same fee by dollar amount.

neither of those things are called "registration fees". And the Statement of Information is bi-annual.

Correct. The OP hasn't responded with more details. Whatever it is that the LLC might be liable for, it can become a legal battle in CA, with the FTB trying to collect tax or fee, and the taxpayer relying on some court case(s) that support the argument that the individual is not liable. I believe this can be affected by whether or not distributions were made from the entity (that could have been used to pay the tax or fee). IANAL. Spidell (CA tax publisher) has a lot of write ups on this in their materials. It's not just a simple case of "Oh, don't worry, you aren't liable".

It's not only court cases, but the statutes in California also make it clear that, under most circumstances, the shareholders/officers of an LLC are not liable for LLC debts, including income/franchise taxes.

There are several ways that personal liability can attach. One is that if shareholders/members (in their roles as such) are paid money that could have gone to creditors, the creditors can get them to pay that money back. But if the money comes in the form of reasonable compensation, it can't be clawed back.