We had a case at my organization where someone created a folder in ArcGIS Server with the special character '&'.
This caused some issues.
One example issue is the fact that when publishers wanted to overwrite their services, their service, nor folders appeared.
None appeared past the folder that was named with '&'.
Looking at the f12 console when clicking on that folder in ArcGIS Server Manager showed lots of errors loading the resource.
Removing this folder fixed it, and allowed publishers to overwrite their services again.
Another issue is this message I got when publishing:
Packaging succeeded, but publishing failed.
Cancel was clicked on connection credential dialog
Again, the fix was to remove the special character.