■ Visual Basic has a limit to the number of disk files it can
  have open at one time. Within the programming environment,
  you are limited to 15 open files at run time.
 
■ Possible solutions:
 
  • Close some of your files. The easiest way is with the
    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.
 
  • Increase the FILES environment variable if the current
    statement is less than 20.
 
  • Execute the Visual Basic command you were attempting
    before. To restart your program, press Shift+F5.
 
■ If you need additional help, move the cursor to a keyword
  and press F1 to open the Help window.