I have a few Windows Forms in my project.  They appear in the Solution
Explorer as, e.g. Form1.vb, and if you click on the plus sign to the left of
it, below it apears Form1.Designer.vb.  Normally, if I double-click directly
on Form1.vb, the form design (i.e. how the form looks, not its underlying
code) appears in the IDE window.  Alternatively, I can right-click on
Form1.vb, and 'Vew Designer' is one option that will do the same thing. If I
double-click on Form1.Designer.vb, I get the Partial Class code for the form,
events, etc.  

Every once in a while, I loose the ability to view that form in the View
Designer mode.  When I double-click on Form1.vb, an empty code window opens
up in the IDE--not the form itself.  If I right-click on Form1.vb, the 'Vew
Designer' option is gone (I can still view the underlying code in
Form1.Designer.vb, though).  This often happens after I've been debugging for
a while, but I've not done anything directly to the project's files (i.e. I
haven't deleted any project files).  Since I can't get the form up with View
Designer, it's nearly impossible to modify the layout of the form, which is
very troublesome.  What's causing this?

The only way I've found to get back the View Designer option is to copy
(e.g. onto the clipboard) the code in Form1.Designer.vb, then delete Form1
from the project, then create a new Form1, and then copy over the original
code (from the clipboard) onto the new Form1.Designer.vb module.  Once I do
this, if I click on Form1.vb, the form will then appear.  However, this is
time-consuming, and it's annoying to have to do this every once in a while.  
How can I stop this from happening?