Happened to me with other wallets. Do you have a large number of small transactions? Reduce the number of coins you try to send to a new address.
have tried 500k now trying 100k man this will take a long time to migrate
edit: 100k dont work too

even 50k wouldnt

edit 2: removing coin control seem to work lol Thanks MarSas!
Try taking off coin control, and send a lesser amount. I think this happens if some coins are trying to mint or recently minted.
I think there is also a way to turn off minting with a wallet setting, but I dont know how to do that.
I think you have to click help, then debug to get the debug window to open.
After that you type this into the debug window and press enter.