WebMethods Designer 7.1 Error

Have someone already seen this error:

com.sun.faces.el.impl.ElException: Read-only expressions can’t be set

I got this error at a javascript running which call an action behind. This action should do a request to the IS, but even not making the request i got this error. I thought i had an error on the action, and the output wasn’t catched but even if my action don’t do nothing i have this error.

Can someone please help me?