The solution to the problem where you cannot send coins mined either from solo or p2pool (tx rejected by network) is to enable coin control in the wallet options, then select all inputs, and deselect any that have under 100 confirmations. The wallet is configured to look at everything as needing only 8 or so confirmations, while this is no longer true. 100 confirmations are needed for newly generated coins. The wallet attempts to send them with under 100 confirms, and the network obviously rejects them.