QBX has a limit to the number of disk files it can
have open at any one time, and your program is at that
limit. Before this command can be executed, you need to
close some of these files.
 
The easiest way to do this is with the BASIC CLOSE
statement:
   1. Move the cursor to the Immediate window.
   2. Enter CLOSE on the first available text line.
   3. Press ENTER to execute the statement.
 
You can then execute the QBX command you were
attempting before. If your program was running, you
will have to restart it.