Losing configurations

[Ref]

Dear All,   I have 7206 high end router which is configured to be used on an ATM network. That means my Serial interface with its sub interfaces are mapped to several Frame relay maps.   Lately, I'm facing many Router down time as when the router is running at the maximum users capacity, no new connections could be established. Even telneting the router is not possible. The consol shows an error stating that not enough memory.!!! I'm going to upgrade and increase the memory very soon. But the surprise is that when I reload the router or power off/on it, I lose all frame relay maps and most of the times I need to re-assign those maps from the beginning. In fact, when the router starts again, FastEthernet 0/0 is administratively down and the serial interface has no encapsulation of frame-relay.!!!!   I understand the lack of memory I have in the router, but why I'm losing the configuration???   Best regards, Ref