Urgent Help needed.

I have designed a monopole antenna with capacitor. I have placed my capacitor vertically upwards with current flowing down to ground. I have tried to run the simulations in 2 different computers and i get 2 different results for frequency.

Even with the same computer, i can have different results when i run the same capacitance value.

Could someone enlightened me on this. Please. I really need this help urgently.