This error indicates that your iSCSI root path syntax is incorrect. The syntax of an iSCSI root path is defined by RFC 4173 to be

  iscsi:<servername>:<protocol>:<port>:<LUN>:<targetname>

Here are some examples of valid iSCSI root paths:

  iscsi:iscsi.example.com::::iqn.1991-05.com.microsoft:snubfin-msdos622-target
  
  iscsi:192.168.0.1:::1:iqn.2000-04.uk.co.fensystems:iscsi-boot
  
  iscsi:10.0.0.5:::1-7:iqn.2010-11.private:winsrvr2008

Note that the <protocol>, <port>, and <LUN> fields are allowed to be empty, and that the <targetname> field may (and often will) contain a colon.