SOLVED !!!!
I had the same problem, on my iMac, I could not solve until today. I have no idea why it worked. Hope by mentioning what I did, someone may figure it out and give us a more comprehensive explanation.
The problem started about six months ago when my iMac OS was updated. Just could not scan to my iMac destination folder anymore; nor was I able to re-setup the destination folder from within the iMac. Tried the latest drivers/softwares; tried the complete driver removal and re-install... to no avail; .....all folders were greyed out when trying to pick a folder destination.
Today, I decided to try setting up the iMac folder from a Windows PC.
Voila! I was able to set up the destination folder for my iMac from the PC !!!!!!!
Don't ask me why it worked!
I suspect the iMac 'Destination Folder' app was not allowed access to my iMac shared folders; that's why all folders were greyed out?
Any idea?