code 45 system too lean/rich

hey all. i got a code 45 on my civic si twice now. its a system too lean/rich prob. i have an aem fuel pressure reg. could running too much fuel pressure make it run too rich??? i have it set at 48-50 psi. is that too much with an intake, intake manifold, header, and exhaust?!?! if anybody has had this prob please gimmeee some info.