Margin warning on Cash Secured Put

Hi all, I tried searching FAQs and couldn't find an answer on this. I have an account with interactive brokers and after placing a trade for a CSP, I receieved a notice asking me to consider adding at least 10% additional margin. Im not really sure why I got this message as I'm not using margin. I have the funds in my account to cover the contract. I ended up just closing the trade because I wasnt sure if interactive brokers would intervene on my behalf. I have a few questions... 1. Why am I being asked to add more funds to the account when I'm not using margin and I have enough money to cover being assigned. 2. Can interactive brokers cancel my trade if they feel I dont have enough margin (even though im not using margin). 3. Would it be better switching to a cash account? I'm using this account for options and have no intention of using margin. Thanks.