SQL Server has difficultly managing memory for systems with a large amount of RAM (say 8+ GB), typically found in 64-bit installations. You might see log messages such as:
A significant part of sql server process memory has been paged out.
Or worse, SSAS may fail to process a cube with the only message that it was cancelled. To see if you have this problem, open Performance Monitor and view “Private Bytes” under the Process category. The value should be less than the amount of physical RAM.
I found this following article useful in dealing with this issue: http://blogs.technet.com/askperf/archive/2007/05/18/sql-and-the-working-set.aspx
You want to configure SQL Server and SSAS to use a specific amount of RAM, but be sure to leave plenty of RAM for OS and other processes, such as SSIS packages. Monitor Private Bytes while you run a typical workload to see how much RAM you can allocate to SQL Server and SSAS. It won’t be surprising if you allocate 2/3 of the RAM to SQL Server and SSAS, and leave 1/3 for the OS and other processes.