The file or folder name contains characters that are not permitted SharePoint 2013. Removing the invalid characters using Regex C#.

Was getting the below error while uploading attachment to SharePoint document library.

string pattern = "[\\~#%&*{}/:<>?|\"-]";
string replacement = " ";

Regex regEx = new Regex(pattern);

string sanitized = Regex.Replace(regEx.Replace(input, replacement), @"\s+", " ");

Helpful post

http://simplyaprogrammer.com/2008/05/importing-files-into-sharepoint.html

Hope it helps