The error is due to going over the bytes limit. Enable coin control, and then you need to select individual blocks with a maximum of 10k bytes (which is approx 67 blocks).
Here's a guide about coin control...
http://forum.xctalk.com/index.php?/topic/161-coin-control-basic-functions-a-newb-friendly-guide/Anyone have an issue with a "transaction creation failed" error? Is there a size limit on the number of Krypt you can send at once or is this issue related to the transaction fee? I am running windows 7 and have a wallet on two different computers and want to simply move all the coins to the other machine to stake there, and I keep getting the error.