Question

Every call of this Function results in a Runtime Error ’13’ Type Mismatch. Why does this happen?

Public Function VersionExists(versionId As String)

   VersionExists = False

   For Each cell In Tabelle2.Columns(1)
      If cell.Value = versionId Then
         VersionExists = True
      End If
   Next

End Function

Answer 1

Here is an alternative as I suggested in the comment

Public Function VersionExists(versionId As String) As Boolean
    Dim aCell As Range, rng As Range

    Set rng = Tabelle2.Columns(1)

    Set aCell = rng.Find(What:=versionId, LookIn:=xlValues, _
    LookAt:=xlWhole, SearchOrder:=xlByRows, SearchDirection:=xlNext, _
    MatchCase:=False, SearchFormat:=False)

    If Not aCell Is Nothing Then VersionExists = True
End Function