"because write access was not granted"

For some time I've been unable to save a picture from Photoshop back to Lightroom.  The popup message says, "Unable to save.....because write access was not granted.  Adobe Support Remote Agents have worked on my computer remotely several times with no success.  Tonight another agent seemed to get things working right.  He went to some 'page' and set everything to 'read & write' and I hit the command key and the 's' key and the photo saved.  After signing off I worked on another photo and tried to save it and got the same popup, "Unable to save....".  Can someone tell me how to get to the page where I can set everything to 'read & write'?  I would be most appreciative.