That loop it is an absurdity.
In the best case if the product of i * j is a negative number the pre-increment of i would always be something other than seven and the post-increment of j something other than nine.
At the other hand. If the product it is a positive number then that's it, the loop doesn't need to check anything else.
For Each ctrl As Control In Me.Controls("pnlMainPanel").Controls
If ctrl.GetType Is GetType(System.Windows.Forms.Panel) Then
For Each subCtrl As Control In ctrl.Controls
If subCtrl.GetType Is GetType(System.Windows.Forms.TextBox) Then
If subCtrl.GetType Is ...