Please provide some additional details.
At what point do you get this error?
What version of DW Are you using?
What is your OS?
What extensions, including the version numbers are installed?
have you tried resetting the workspace layout:
go to Window -> Work Space layout -> Reset '<your layout name>'
and Delete the Dreamweaver Cache file from the users configuration folder:
have you tried using Image resizer on a new blank php page with only an image on it?