Can you post a screenshot of what your "Edit Background Proteome" dialog looks like?

The "Add File..." button is supposed to become enabled depending on the text in the "Proteome file:" textbox.

The message at the bottom of the Edit Background Proteome dialog is supposed to tell you what is wrong (if anything) with the file that you have chosen (file does not exist, not a valid background proteome file, etc).

Dear Nick
I attach you the screenshot of the "Edit Background Proteome" pane.
Thanks
Cristina

I believe Skyline thinks that your .protdb file on the Z: drive does not exist.

In Skyline-Daily, the text in the "Proteome file:" textbox will turn red to indicate that Skyline could not find the file, but in Skyline 3.7, it looks like what your screenshot is.

I cannot think of a reason that Skyline would think the file did not exist. I wonder if it might have something to do with case-sensitivity (that Z: drive is probably a network share on a computer that might care about the capitalization of filenames, even though Windows usually does not).

I wonder if this is just a temporary condition-- Skyline tried to check whether the file exists, and, for a brief moment perhaps, Windows said the file was not there. You could make a small edit to the Proteome file textbox (e.g. inserting and deleting a space) and Skyline will once again check whether the file exists and may enable the buttons for you.