userform - help needed

[Elane]

Hello to everyone.
I created a userform (UserForm1), and inside this form I placed 20 textboxes and 20 checkboxes.
Everytime I make the userform to appear, I need all the checkboxes to be false and all the listboxes to be empty
One question at a time...
I can write down 20 rows to set each checkbox value=false but I would like to have something better
I tried

For i = 1 To 20
    UserForm1.Controls("CheckBox" & Chr(64 + i)).Value = False
Next i

but it says runtime error, impossible to find the specified object
These instructions are placed in the command button macro, just before the UserForm1.show line

How can I fix the error?
Thanks to everyone