Double check you got the right PC100 memory. You can also use PC133 as well.
I used some MemoryMasters ram I got off of Ebay.
I think I spent like 30 bux.
If you can, open er up, and get some contact cleaner, and compressed air in there.
Clean out ALL the contacts, cartridge connectors.
I was able to scrub mine down with a super soft bristle tooth brush to break apart some of the oxidation on my dimm's contacts, and slots.
That helped me a lot because I was having a similar issue.
Also in another thread we've been talking about power.
Make sure you are powering your Naomi 1/2 adequately.
There's loads of shit faults with these when they don't have accurate 3.3V.
Attached is a picture of mine.