Question is not clear , errors will get due to many reasons at same time you are not mentioned the error also.

As Rama mentioned can you mention the error and if possible the antenna model as well.

I have assigned micrsotrip feedline excitation after going through link provided by Monyer Al-Fatlwai. When i give validate all I get no errors and warnings. But when i simulate the design I get the following errors

Project3 - Copy (C:/Users/SONY/Documents/Ansoft/)

HFSSDesign1 (DrivenModal)

[info] Port refinement, process hf3d: '1' conductors touch lumped port '1', typically a lumped port contains 2 conductors. Please verify conducting boundaries and objects are correctly assigned and touch the port. If a Radiation boundary touches the port and it is desired for use during the port solution, select 'Use Radiation Boundary on Ports' under the Advanced tab in the Solution Setup. (10:01:38 AM Apr 24, 2017)

Also when I Change dimension of the strip line, The resonant frequencies i am getting won't shift only the return values changes. I have designed the antennas for 2.4Ghz Please help regarding whether the procedure i followed for excitation is correct or not.

I have attached the hfss file i simulated and graph obtained for reference.

Thank you all

Move your boundary away from the port and then excite, it should work