Model Optimization Problems

I am trying to optimize a model using Optimize pro, however, I am always getting the error as follows;

GRG232 6.06 Report: Date Mon Mar 29 17:21:18 2010

Problem Title: VisSim32 Version 7, Optimization by VisSim32 / OptimizePRO

FATAL ERROR IN VARIABLE BOUNDS: xub[11] = 0.12 < xlb[11] = 0.22

FATAL_EXIT: GRG2 terminated by a FATAL ERROR. INFORM = -1

Time used is 0.047 seconds.

Anyone have an idea?

Thanks

Brian

What is xub[11]?