When you upload a file to an item in an Agenda, you cannot have any special characters in your filename.
Accepted characters include:
Lowercase letters
Uppercase letters
Numbers "0 to 9"
Accepted special characters: ~ ! ( ) - _ = [ ] { } , .
If you have a special character in your filename that is not accepted, you will receive a message that states: You have an invalid character in your filename. It will also list the accepted characters.
If you receive this message, you must rename your file on your computer and re-upload it to the item.