It's basically a message telling you that you're running SQL Server on a grossly underpowered machine. 2gb is just the bare minimum to get the server started. You need more memory.
What happened is that you had some data in cache and then a query was run requiring all the memory to be flushed out to disk in order to load data from the new query into memory. This will keep happening.
Get more memory.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning