Mac OS wont open a file if the App is open - Need to quit the app every time to open files Long time Mac user but never had this problem before and it's driving me nuts.


Every time I open a file by double clicking on it, it will refuse to open if the application is already open. Weirdly it will do the quick icon expanding flash you see when you open a file, but it wont load.

I will need to quit the app, then open the file again for it to open. Then, once in the application I can select open from the pull-down menu which works.

It is happening on all types on applications not just one, Photoshop, Excel, Word, Preview, Quicktime etc

I then attempted to show this to a friend and it completely stopped happening for a few hours (sods law) at that moment! It does seem to momentarily start working again. 

How might I resolve this weird behaviour?
There's a few things to try here to help us narrow down this problem.

Boot into Safe Mode

Follow these steps to boot your Mac into Safe Mode:


Fully shut down your Mac
Restart your Mac
Immediately press the Shift key and keep it down 
Let go of the Shift key when you see the login window 
Now log into your Mac and (NOTE: If you have FileVault enabled you may need to log in twice)
Now test to see if you have the same problem
Exit Safe Mode by restarting your Mac as normal
Once again, test to see if you have the same problem


Once you've done this let me know how you went and we'll go from there.