California has three different identifying numbers for their business returns.
You can use the California Secretary of State website to determine your entity's California ID number and type.
In March of 2017, the California Secretary of State began issuing California Corporation Numbers that begin with a '4'. The existing CA electronic filing schema does not allow for electronic filing of returns where the California Corporation Number begins with anything other than 'C'. If your number starts with '4', and you need to file a 2014, 2015, or 2016 return, it will have to be paper filed. The California Franchise Tax Board (FTB) will update the schema for 2017 and future years so that these returns may be electronically filed.
The FTB has stated that, if you are required to file electronically but have a number that begins with '4', you will need to file a Business Entity e-file Waiver Request and indicate you cannot file electronically due to 'technology constraints'. If you have any further questions, you should contact your account manager or email the business e-file coordinator mailbox at email@example.com.