I also have problem with the slash syntax. I am trying to update attribute with a string
https://servername/path/%'givenName'%.%'sn'%.jpg and it fails. when I put space
/ %'givenName'%.%'sn'%.jpg then it works.
RFC4517 http://www.faqs.org/rfcs/rfc4517.html states that it should be represented with %x2F
SLASH = %x2F ; forward slash ("/")
but when I use %x2F%'givenName'%.%'sn'%.jpg I get value
So obviously ADmodify doesn't have full implementation of LDAP syntax.