QuickBASIC 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. Type CLOSE on the first available text line.
  3. Press ENTER to execute the statement.
 
This lets you execute the QuickBASIC command you were
attempting before, but if your program was running
you will have to restart it.