I've searched the forum on this issue and can only find instances of this error where network sharing is enabled; in my case there is no network sharing (i.e. the Server service is never started). You will be familiar with the behaviour on opening multiple instances of Excel 2010 where the new Blank Workbook shown changes automatically from Book.xlsx to Book2.xlsx then Book3.xlsx and so on. I want to customize the default Blank Workbook (lets call it Zbook.xlsx) and every time I open an instance of Excel have it load the same way as above i.e. Zbook.xlsx, Zbook1.xlsx, Zbook2.xlsx. etc. To achieve this I have tried saving Zbook.xlsx in XLSTART however on the second and subsequent instance of Excel I get the error "Zbook.xlsx is locked for editing". Clearly, on this occasion, Excel can't create a Zbook2.xlsx. Without having to click through some sequence (like File>New>MyTemplates) how can I have Excel automatically open a sequentially numbered Workbook? For example is there a way to permanently change the makeup of the default Blank Workbook? Thank You!