TypeError: Object expected at eval code (eval code:1:1)

On Task entity form save I got the following error

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TypeError: Object expected at eval code (eval code:1:1)
   at RunHandlerInternal (adzz.adzz.com/.../ClientApiWrapper.aspx)
   at RunHandlers (adzz.adzz.com/.../ClientApiWrapper.aspx)
   at ExecuteHandler (adzz.adzz.com/.../ClientApiWrapper.aspx)
   at Mscrm.TurboForm.Control.CustomScriptsManager.prototype.$BQ_1 (adzz.adzz.com/.../formcontrols.js)
   at Mscrm.TurboForm.Control.CustomScriptsManager.prototype.executeHandler (adzz.adzz.com/.../formcontrols.js)
   at Mscrm.TurboForm.Control.CustomScriptsManager.prototype.executeHandlerByDescriptor (adzz.adzz.com/.../formcontrols.js)
   at Mscrm.TurboForm.Control.ViewModel.FormViewModel.prototype.fireOnLoad (adzz.adzz.com/.../formcontrols.js)
   at Mscrm.TurboForm.Control.Data.DataEntity.prototype.$I4_1 (adzz.adzz.com/.../formcontrols.js)
   at $v_6 (adzz.adzz.com/.../formcontrols.js)

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how can I find where the problem is ?

Thanks in advance,