The working set of a process is the set of memory pages currently visible to the process in physical RAM memory. These pages are resident and available for an application to use without triggering a page fault. While increasing your working set size can reduce paging for your application, it can adversely affect the system performance.
VFP is know in using all the memory it can get. One of proactive steps in reducing memory usage is limiting VFP buffers size using SYS(3050) - Set Buffer Memory Size. It's a good idea to empty the working set when your application goes into a wait state. It can be done by calling EmptyWorkingSet Function or SetProcessWorkingSetSize Function and uses GetCurrentProcess Function.
The explanation for the error isn't too helpful and even confusing as the error often shows up on computers with plenty of memory.