FWIW- i bought a X10 SRL-F about a 9mo ago from a different ebay seller, and i too sometimes see the ram slot error on post. Its actually been quite a while since ive seen it, but even with verified good ram (ie memtest many days) and RAM on the boards QVL, i still have seen the SLOT xyz error a few times, on this paticular board/model. (the entire board / system runs fine once its booted though, i mainly use it/this system to test HDDs though, so it will be off for months at a time).
i dont see this on my other SM systems (i always use QVL ram though, anywhere)