Notepad++ says "Check if file is open in another program" - but no other program is open

Solution 1:

Had the same problem when setting up apache webserver and php. Found out that this is due to the UAC in windows 7. It's is not because you have the file open anywhere else. Try opening Notepad++ as administrator. Either right click Notepad++ shortcut and choose run as admin or ctrl+shift and click notepad++ shortcut. Then open the file you want to edit from within notepad++.

This solved the problem for me.

Solution 2:

One possible problem is that the file is open via the explorer Preview pane, select a different file in the preview pane or disable the preview pane completly.

I just had this issue and it was due to having the file selected inside of Windows Explorer - the directory browser. It shows a preview of the file and I guess that causes Notepad++ to see it as being open.