The title says "function" but the body of your email says "form". When
you copy-paste a form it's easy to get into strange errors. What I
advise you do is go to form A in the solution explorer, then press go
into the code and make sure the line at the top of the file reads:
private class FormA
Then go back to the solution explorer, hit the expand key beside the
form and edit a file which would be named FormA.designer.vb Then make
sure it's also has the line
private class FormA.
Then go to form B and ensure those values are both different from the
ones above.
If you refer to the file name:
Menu Tools -> Options: Projects and solutions -> General: "[X] Prompt
for symbolic renaming..."
Referring to the class name in the property window:
Menu Tools -> Options: Windows Form Designer -> General: "[ ] Enable
refactoring on rename"
(I wished there was an "ask" option in addition to True and False)