A transaction is in the memory pool ("mempool") if it is known about by the node, but has not yet been confirmed in the blockchain. Your problem is probably that mining has stopped, and the most common reason for that if you have a blockchain with mining-requires-peers=true, you have given mining permission to more than one address, but your node is not actually connect to any others. To fix this either:
- Re-run multichaind with -miningrequirespeers=0 as a command line parameter.
- Remove the mine permissions from all but one address belonging to this node.
- Connect another node to this one.
Note also that the newer protocol (supported by 1.0 alpha 27 if you make a new blockchain) does not require assets to have their issuance transaction confirmed before they can be transferred.
