The server is Lenovo with a Xeon E5620 CPU (8 cores at 2.40 GHz), and RAIDed hard drives. The server is running SBS 2011, and was recently (at the start of these problems) upgraded to 16Gb. We upgraded to this server in 2011. At ACs suggestion we installed AC in a VM. I have experimented with memory allocations between the server & the VM. The VM never goes above 3 Gb in use.
How much disk space is available in the VM? If you recently upgraded to 16GB RAM and started seeing the issue. It could be that your hard drive is near capacity. (Adding RAM increases the size of the page file and the hibernation file by an equal amount). Extremely common issue for people with SSDs to overlook. They wonder why half their capacity is gone when they upgrade to 16GB of RAM.