Problem with mesh error in HFSS 10.1.3 simulation

whenever I do simulation in HFSS10.1.3, the mesh error always exists (Please see the attached figure)
I design a L x H (14cm x 7 cm) antenna in 10 MHz. The sweep frequency is from 5-15 Mhz which means the radiation box should be at least 1514 cm. The "validate check" is ok; howver, as I run the simulation, it pops out mesh error.

why? Who can help me? thanks!

the antenna seems too much small regarding the wavelengh at 10MHZ namely 30 meters. Is it really gona work? (Antenna aperture)/lamda^2=1.8e-5
I think you should seed the mesh on the antenna with a very small fraction of wavelength