>I am getting a random failure when INSERTING (INSERT SQL) records into a DBF using a DLL on a Server. I have even trapped the error and dumped the actual INSERT string to a File, which I later run in the Command Window and it does not fail.
>The INSERT includes a memo field which could be rather big (say 10k). The error itself is: "User-interface operation not allowed at this time. (Error 2031"

In all likelihood, the INSERT is generating a warning message or error that you are not trapping; the message box is a UI element, and an in-process server in VFP (a DLL) may not use any UI elements, and when it fires, the DLL shuts down, which you do trap. You need to trap the condition that triggers the warning so that it won't fire the messagebox.