Unable to save a file in the same directory

R2D2

Hi everyone:

I'm using BC 2.5.484 on a PC with Windows 8.2 over Dropbox and works nicely, but sometimes when I open a file, normally a Excel file, the MS application say that is unable to save the file with a different name in the same directory. So, the only way to save the new file, is a 2-step process, first, save the file on a different directory, and then move the file to the previous and encryp directory.
Is this a bug? Is this normal? Is there any problem with this configuration?

Thanks to everyone and happy new year from Spain!