A 20 Amp GFCI breaker was installed into a new service panel to service the kitchen in an old house. The kitchen electrical boxes were two small to fit GFCI receptacles. When a two prong device, a light, mixer or microwave is plugged into this circuit the GFCI breaker trips. What may be the problem?

Describe wiring connections made during installation of GFCI breaker.

I agree, this sounds like a circuit breaker incorrectly installed...

Please also add a description of the breaker you removed. Was it a 20 amp breaker (expected) or a 15 amp breaker (as in an older home).

My concern is that if you had 15 amp circuits installed and you replaced a 15 amp breaker with a 20 amp GFCI breaker without changing the wiring from 14 AWG to 12 AWG you may have created a ripe situation for fire.