unable to upload a sketch ?

i have an arduino UNO

it has been working fine but has been a bit slow to repsond and be found as com port 6 when you plug it in

i loaded a new sketch and it seems to be working on the arduino

but every time i try to program it again - it tells me com port 6 is in use ?

any idea's ? it is driving me nuts

i managed to load a new sketch by holding down the rest button and letting it go as the sketch size appeared

but i am still unable to open the serial monitor

it says the port is in use ?

problem fixed

i kept pluging the arduino in with the reset button down and letting it go just as it compiled before the write

eventually it started to work normally again

hope it is a one off !