■ When you switch between the programming environment and the
  Form Designer, Visual Basic creates a temporary file which
  communicates project information between the two
  environments. This file could not be created.
 
■ Possible solutions:
 
  • Delete one or more files on your hard drive to free up
    disk space.
 
  • Make sure you are not running Visual Basic or the Form
    Designer on a read-only drive.
 
■ If you need additional help, move the cursor to a keyword
  and press F1 to open the Help window.