Hi!
I didn't have the same message (I've disabled the warning message reporting...) But I've struggled to get a new password sent. Instead of sending the email with the new password, I always got to the frontpage, without a correct Itemid, and nothing happened.
Your post made me think that it may be a compatibility issue between the LostPassword function and the CB_peoplesign Captcha plugin... And it's the case! They don't seem to work properly together. So, I installed CB Recaptcha plugin and now it's working fine...
Thank you, although I may not have answered your question, you have answered mine! And I've been looking around in the forum for quite a long time!
Greetings,
Phil