Did you select the special character (the vertical line before and after the number) from the symbol table? If so, make sure you are picking the same one that is in the document -- if you look in the Windows Character Map, there are several vertical line characters. If you search on a different vertical line character than the one that is in your document, the search will fail.
A better way to do this search might be to manually search for one occurrence of the string, highlight and copy the entire string, then paste that into the search window. In this way, as long as the same vertical line character is used every time throughout the document, you will find it.
Also, are you sure that there is a vertical line character both before and after every single occurrence of this string? If you aren't sure, then you would be better off searching for "10480", and then visually inspecting each one you find.