Run-time error 91 object variable or with block variable not set

[JUST ME]

Hello all,

I am having trouble with Run-time error 91, I created the code in a document by it self it worked fine. once i moved it over to my actual project it gives me the run-time error 91 and i have spend hours trying to determine why it works when it's the only code in a document but not when i put in in my project with all the other codes. the error occures on "userform1.show vbmodeless. does anyone have any suggestions?

Private Sub Document_Open()
Application.WindowState = wdWindowStateMinimize
UserForm1.Show vbModeless
End Sub