|Crucial may have been reading the SPD chip on the ram stick and not seeing it through the OS.|
In any event, the stick is either bad or incompatible with your system. It looks like it originally came with PC2100 ram. You probably put in something faster, which is usually OK but there are limits. There could be a density problem too wherein the motherboard chipset isn't able to work with ram chips having a large memory capacity.
Check at crucial for compatible ram specs. They're usually right. Buy it from them or check ebay or computer shops.
Now that's what I call a sticky situation