What are you running?

I've seen this type of error on a Solaris box running Oracle 9.x and Using the Itelligent agent. The dbsnmp process has a memory leak on SOLARIS boes only which gobbles Swap space until it consumes it all... then the server grinds to a halt.

If you are on Solaris, do a top and see how much RES memeory the process is using. It it's using copious amounts, Kill this process to an see if it makes a difference. The process will automatically start after it's killed.