This firmware update tightens the specs for RAM in Macs so they will be more reliable but it means that some older RAM is excluded. It caused this problem for a lot of people when it first came out a few months back.
First thing you should try to do is call the vendor you bought the RAM from and describe the problem and ask for a replacement module that is up to spec. A lot of vendors will replace it for you free of charge, except for maybe shipping.
If that doesn't work then try using DIMM First Aid
to patch your unrecognized DIMM so it will be recognized. Only do this as a last resort if you cannot get it replaced however, since if slows the timing and could affect performance and it is not guaranteed to work.