Difficult to tell you why your mn sometimes stops working, without seeing what you put into the conf.
Your question regarding "insufficient funds" is easy to answer, though. When you start your mn, the 250k coins gets locked so that they can't be spent accidentially while the mn is running. Solution is to enable "Coin Control" in the wallet options and go to "send" and click on "Inputs". You can then unlock the 250k and sent them.