Cubase 6 multitrack recording from Behringer X32 usb problem

Hello. I have a situation(sorry if my english is not so good) . At my church , we have a Behringer x32 mixer and i’m using my Sony Vaio i3 and Cubase 6 to record from the usb port of the Behringer 20 tracks simultaneous. When i start the recording , everything is ok but after 30 minutes if i leaved it on like an hour or 2 depending on the church program , when i stop it and try to save , everything goes away. I try to lower the buffer and to select 16 bit recording but no rezults. The only thing i can do it’s to start the recording 20 min , after that stop it and save and then again 20 min , and so on. But it’s very unconfortable cause the services are 2 hours. What can i do ? My Vaio i3 it’s not powerful enough ? Or the usb conection it’s not good enough for 20 tracks simulateous ? Or my hard drive ? Should i record to an external usb drive ? Thanks you !

Important to know: which OS are you on and is it 32 or 64 bit Cubase?

Sony Vaio , i3 , 4 gb ram , windows 7 home 64 bit.