What is causing the active sheet reference?
Using the Address property - though explicitly addressing the project's Sheet (Code)Name Sheet3
.RowSource = Sheet3.Range("B2:C21").Address
will only assign the cells' range address "$B$2:$C$21", not the tabular worksheet reference.
To get the full reference Sheet3!B2:C21 you could either set the External argument to True via
Sheet3.Range("A1:B7").Address(False,False,External:=True)
or prefix the range address string by the worksheet Name plus !
Sheet3.Name & "!" & Tabelle1.Range("A1:B7").Address(False,False)
Further issue
As you mentioned Error 70 ("permission denied"), it's very likely that you have further
code trying to add rows to the listbox'es .List property which doesn't get on well together.
Personally I'd do without .RowSource at all and handle the listbox list via array assignments or use an intermediate hidden sheet with rowsource data you can manipulate.
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