What is the difference between Imams an Nawawi and Ibn Hajr and the innovators?

Shaikh Rabee explained it nicely ( from http://salafitalk.net/st/viewmessages.cfm?forum=25&topic=4564 ):

Shaikh Rabee Bin Haadee Al Madkhalee (hafidha-hullaah) also stated:

(Not) everyone who falls into bidah is declared an innovator; because if we
were to adopt this principle, we would make Tabdee of the majority of the
Imaams of Islaam.  Shaikhul Islaam Ibnu Taymiyyah (rahimahullaah) said:

‘Indeed many of the Salaf and the Khalaf fell into innovation without
being aware of (it); either (due to) acting on a weak hadeeth or
understanding the text (in a manner) other than what Allaah and His
Messenger intended, or (due to) Ijtihaad.’

At present we have Imaams of Ijtihaad; and his/their Ijtihaad (can) lead
him/them to mistakes or innovation.  So, if we know (him) to be of a
sound Manhaj and sound intent, being far removed from desires and being
eager for the truth; if we know this about him and he falls into
innovation, he is not declared an innovator.  
                
But if we know him to be upon desires and evil intent, and we know of
affairs about him showing that he desires innovation, he is declared an
innovator.  You find them (Salaf) passing the judgement of Tabdee on many
people due to this.  

And many people fell into bidah but were not called innovators; because
they (Salaf) were acquainted with their sound and good intents, their
eagerness for the truth and the soundness of the Manhaj they traversed.

[Quoted by Shaikh Ahmad Baazmool in ‘Siyaanatus Salafi Min Waswasati Wa
Talbeesaat Ali Al-Halabi’: page: 165]