IE error: Unable to load requested language file

[eluser]daninfpj[/eluser]
In a rapyd dataedit form after submitting I get:

An Error Was Encountered
Unable to load the requested language file: language/validation_lang.php

Solved it temporarily removing the validation rules but of course that's not a nice thing to do.

It only happens in the dataedit form, in IE 7 (works in FF 2), don't know how does it behave in other browsers.

Any help appreciated.