https://www.dotnetzone.gr:443/cs/blogs/birbilis/archive/2014/04/04/gotcha-system-io-getinvalidpathchars-result-not-guaranteed.aspxat System.IO.Path.GetInvalidPathChars one reads: The array returned from this method is not guaranteed to contain the complete set of characters that are invalid in file and directory names note: can also call this method from non-trusted SilverlightelCommunityServer 2.1 SP3 (Build: 20423.1)