Cubase LE 6 stop working when export audio mixing

Hi, i’m a newbie here and this is really the first time i’m using this music production things software and no have any idea how it really works.
I recorded a vocal and accoustic guitars following the tempelate and all the things were done right. I can hear the sound from ear in monitor and i want to export it to .wav files but suddenly it stop working.
No error message, just stop working then close the program button shows up.
What i did is following on youtube like select the track: ctrl+a and press P then click export>audio mixdown
Name the file and choose path, then select stereo output and change bit rate into 16-bit
Then i click export and cubase stop working

Please help…
Thank you.