what's wrong with my code?

hi,
I’m a beginner of cocos2dx, and I’m writing some codes to study it based on Xcode 4.2 + iOS 5 SDK.
I found CCRepeatForever::actionWithAction() only accepts CCActionInterval* as parameter,
but CCSequence::actions() return CCFiniteTimeAction.
so if I wrote like below:
CCRepeatForever::actionWithAction(CCSequence::actions(a,b, NULL));
I will get error again.

How can I combine CCRepeatForever and CCSequence?

thanks for your help?