When logging in to an FTP server, many often change the intial directory to a user-specific directory. Based on the error, the IS service is assuming that the current directory is the root (httpdocs) but that may not be the case, thus the relative path specified in the get is invalid.
Try either an explicit cd before the get or an absolute path in the get.
#webMethods#webmethods-Protocol-and-Transport#Integration-Server-and-ESB