Ok, the total wattage for the new dimmer must be 60 watts or more per dimmer, if not it will cause problems.
Also, if the lights are low voltage and use a transformer, this too can cause issues on some dimmer types.


Also, as another point apart from your current issues....
I presume your old dimmer was a NON metal face plate and the new one is metal.
If this is the case, you will need a proper earth connection installed.
Dont assume the earth wires you have are earths as they will need proper testing.