korg legacy collection

hi
 
when i use ms-20 (korg legacy) vsti on sonar 8.5  on 128samples of asio
it hangs(crash ) in about 10 minutes..(playing keyboard about 10 mintutes)
 
but when i use it on 512 samples of asio  
it never hangs(crash) and ok ..
 but i feel some latency on my keyboard...
(so i wanna use it on low latency)
 
i've tried every options of the vsti settings
but had no luck
 
well my audio card is m-audio delta 192
also i've tried it on several laptops and audio cards too...
but the same result...
 
does anybody knows this issue?...
 
also i've tried the same on cubase it never hangs...