Python IDLE subprocess error?

Question

IDLE's subprocess didn't make connection. Either IDLE can't start a subprocess or personal firewall software is blocking the connection.

Don't think this has been asked-how come this comes up occasionally when running very simple programs-I then have to go to Task Manager & stop all Pythonw processes to get it to work again?

It seems to happen randomnly on different bits of code-here is the one I'm doing at the moment-

f = open('money.txt')
currentmoney = float(f.readline())
print(currentmoney, end='')
howmuch = (float(input('How much did you put in or take out?:')))
now = currentmoney + howmuch
print(now)
f.close()
f = open('money.txt', 'w')
f.write(str(now))
f.close()

Sometimes it works, sometimes it doesn't!