arduino work one time

[talaviv]

hello

i have arduino mega  I have connecting it to labview and it work at first time but when i connecting it the second time it dosn't work

becuse it doesn't see the device so i restart the computer when i connecting the mega but it work on time only

and when i change the COM # it doesn't work and have this error

if any one have any suggestion i will be thanks for him .