Galloway is getting it in the teeth primarily for his support of the Allawite (Shia) leader Bashar Assad during the the on-running Sunni-Shia civil war in Syria (as well as for his parallel support for Shia Iran).
(These internal disputes within Respect began the moment the party was formed by various renegades of the Trotskyist/'progressive' Socialist Workers Party. That's what ideological purity, mixed with cynicism and opportunism, will necessarily lead to.)
In other words, the Stop the War Coalition isn't against war at all. It's only against 'Western' or 'capitalist' wars. Mass murder and oppression carried out by brown or black people, or when carried out by Leftist regimes, does not even register in the Trotskyist or Progressive mind.
*) Some examples of John Rees's work for Iran via Press TV: