Quote from piezoe:
Donnap has the right answers for you. Many brokers allow you to trade most option strategies in a cash account, even in IRA's. One exception of course would be any trade with an undefined risk. But that does not apply to your trade, but if you were trying to leg in by selling the short leg first, or even if you submitted both legs as separate orders simultaneously, which is what i suspect you did, it won't be allowed in a non-margin account. The reason is simple, if there is any chance that the short side will be filled before the long side then a disallowed position results. The way around this is to submit the long leg first and fill it. Then submit the short leg order. That will be allowed in a cash account. An alternative is to submit the orders linked together as a vertical (spread). Then both sides of the order will be filled simultaneously and your short calls will be "covered" by the long calls.
Your problem really just boils down to how you submit the order.