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Form already displayed; can't show modally (Error 400)
You can't use the Show method to display a visible form as modal. This error has the following cause and solution:
· You tried to use Show, with the style argument set to 1 – vbModal, on an already visible form.
Use either the Unload statement or the Hide method on the form before trying to show it as a modal form.
btw: uz to "možda" može biti problem kod zaštite ( možda u kodu da napraviš provo unlock a potom ponovno lock ) nadam se da si me shvatio a možda i nisam u pravu
pogledaj link
How to run a VBA macro on a protected sheet
protect sheet i vb greska 400