"Transaction too large" means that it has too many inputs and it's larger than 100 Kb. Such transactions are not allowed. Most likely you have tons of tiny inputs from mining or smth. To solve this please either try smaller amounts (like 10x smaller or so) or use Coin Control to select inputs manually (it will also tell you when the size is too much). If you are not familiar with Coin Control please see explanation there https://dashpay.atlassian.net/wiki/pages/viewpage.action?pageId=1867831