There is no official limit, as far as I am aware. But you will need to explain the reasons you cannot handle your finances to the creditors and, I imagine, their patience might wear very thin!
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014
Foggy is right. We regularly propose second and the odd third IVA for people but you do need a valid reason. HMRC in particular do not like this so if you self employed you would need an even better explanation.