When attempting to attach files to lists you may receive the a dialog box stating “File names can’t contain the following characters:  & “ ? < > # {} % ~ ?/.”.  This is recently been noted as an issue with the August 2015 cumulative update for SharePoint 2015.




As I understand it Firefox and perhaps other non-Microsoft browsers do not produce the error, although I have not tried all the other browsers myself just yet.

The September CU does not fix this issue.   For those that have applied, you will therefore need to backout to the July 2015 CU, or patiently wait for perhaps the October 2015 CU.  No word yet on whether the October 2015 CU addressed the issue.