Your program has opened more disk files than QBasic can
handle. You must close one or more of the open files
before you can use QBasic commands.
 
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 QBasic commands. If your program was
running, you will have to restart it.