Complex frequency solution when doing eigen mode analysis on coupled microstrip

I tried to do eigen mode analysis on coupled microstrip resonant MR RF coil using HFSS and simulation was complete but i found that adaptive passes didn't converge and i got solution in complex frequency. i am little bit confused. can somebody provide me any information or links so that i can correct my simulation.

when i simulated lossy material using eigen mode, I got the similar result in complex frequency either...I don't know the reason either..