The file (or folder) name is invalid if it contains one of the following characters:
- tilde (~)
- number sign (#)
- percent (%)
- ampersand (&)
- asterisk (*)
- braces ({ })
- backslash (\)
- colon (:)
- angle brackets (< >)
- question mark (?)
- slash (/)
- pipe (|)
- quotation mark (")
See http://support.microsoft.com/kb/905231 for more details.
Also, the the total length of the URL path to the uploaded file or folder must not exceed 255 characters.