The circuit breakers are tripping occasionally.  What is wrong?

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When a breaker is tripping, it is because it senses an overload or short circuit condition.

Most breakers used (and the breakers in your application) are rated up to 240 VAC (and/or 65 VDC depending on application and breaker used). 40C ambient room temperature
They are rated to carry their rated amperage without de-rating; although de-rating is always recommended to meet NEC requirements.
Based on this breakers trip curve, when the breaker senses an overload of only 35%, it will eventually trip (between 55-750 seconds).

If the breaker trips instantly EVERY time, then it is sensing a short
If the breaker trips instantly every 3rd, 5th or 20th time, then that is indicative of in-rush current. 
If the breaker is tripping over a period of time (could be 15 minutes) then it is an overload condition
The breaker protects what is wired after it wiring and ?load?.

Knowing the voltage and amperage on the circuit in question is important to know.
As a rule of thumb, incandescent lamps are resistive loads and are fairly simple to deal with.
When capacitors and other electronic components are introduced, performance variables may fluctuate.

Nuisance tripping is usually the result of one of two conditions
#1 - In-Rush Current
You can eliminate in-rush current every time by programming the dimming system to turn on at ZERO volts. (Or Manually turn the dimmer on with the slide at Zero and ramp up manually)  Never have it turn on where it was turned off, but have it reset to 0 volts and ramp up to some specified level over a 2 second period.  In Rush current will typically dissipate within 3-5 cycles, One cycle is (1/60) .0167 seconds, 3 cycles = .05 seconds
If the load is turned on with full voltage being energized, Inrush current can easily be 10-25+ times rated current depending on its severity.
When it is overloaded 12 times (1200%) ? this breaker is rated to trip between .008 - .038 seconds.  

#2 - Breaker is not de-rated
Even though the circuit breakers can be fully loaded, it could lad to nuisance tripping on an unregulated circuit.  
There will be a youtube video posted that shows the impact on load when the voltage to load fluctuates.
The NEC states 80% load is best on circuit protection and this is one benefit when doing so; reducing chances of nuisance tripping.

(If I ever have a unit with two identical breakers and one load is working fine, I will swap breakers. 
Always measure Voltage and Amperage  on the circuit in question
Once these basic parameters are know, it is then trial and error to pinpoint the exact cause of the tripping.