It just means your memory modules don't have a Serial Presence Detect chip. This chip is programmed with the rated speeds and timings the modules can handle so the BIOS can automatically configure it. If you manually configure the memory settings, then the SPD doesn't get used. But without a SPD, if the BIOS isn't configured manually, it may default to the slowest settings.
Pretty much every module has a SPD these days. What kind do you have? Is this a new board or memory or has it suddenly started happening with a working system?