Ajax TruClient : Error When logoff and relogin in same iteration

Its like

Homepage--> Login --> dashboard-->logoff-->homepage 2-->login 2--> dashboard 2 --> Logoff 2

This all is single iteration , this is just to check response time impact of cache.

however truclient script is failing at dashboard 2 with some 500 technical error while manually its working well.

any guess why this is happeneing ? anything to be taken care to make it working

Thanks
Ani.