Optimization LPDA in CST

Hello. I have planar LPDA in CST. Freq. range 700 MHz - 3GHz. I modeled and simulated this antenna in CST 2016. But result for lower freq. is bad and also Sparameter isn't under -10 dB. So I must optimize this antenna and here is the main problem. I set in Optimizer parameters which a want optimize (firstly i decide to optimize length dipole elements LPDA), after that i set Goals i choose S11Parameter and I add condition -10 dB and frequency range 700 MHz to 1850 MHz. 1850 MHz is central frequency so i decide use this like maximum, because i need optimize lower frequency. After this settings i click on start and CST give me this error:

I don't know where is a problem and i am distressing from this.

Thank you buddies. For help.

All set parameters:

i dont get what you trying to say here! your min freq = 700MHz and mx freq = 3GHz. i dont understad why you set it to your centre freq which is 1.85GHz. you should set it to 3GHz!