The brackets are used by Excel when putting together the links to other files.
When you later save and again open your workbook, Excel will recognize the self-referential links and delete them.
Another way you can find links is to search for either the left bracket ([) or right bracket (]) in your workbook.
If you do, this is a good indication that the button or graphic is linked to a macro contained in a different file.
If you delete the button or graphic, or change the macro assignment, the link problem should go away.
First, choose Links from the Edit menu, if the option is available.
(It will only be available if Excel recognizes explicit links in the workbook.) From the resulting Links dialog box you cannot delete links, but you can change the links so that they point to the current workbook.In Excel, you can create a drop down Data Validation list, so it’s easy to enter valid items in a cell.Usually, the list of valid items is stored in the same workbook, but it’s possible to set up a drop down from a list in another workbook.Important Note: For the data validation to work, the workbook that contains the list must be open, in the same instance of Excel.Users will have to open both the workbooks — the one with the drop down lists, and the workbook with the original source list.It can be frustrating to open an Excel file and be continually asked if you want to update linked information, particularly if you are not sure what information is linked.