problem with UA-25EX with inputs and cubase

hey
when i am opening a cubase project and i am connecting the guitar to the input i have a problem
everything its works ok until i quit the program and trying to open the program again
when i open it again the asio duplex beacome the sound driver and when i am trying to switch to the UA-25Ex its telling me
"the driver is not connected please connect the driver"
i have been trying to reinstall the drivers over and over again without no succes
what can i do ?
thanks