A 6 month admin period is built in to standard Ts&Cs as a matter of course. Most firms take a couple of months, some take a couple of weeks. But, a couple take the full 6 months.
Some delay could be down to awkward creditors putting in different claims to thse originally agreed, which has to be sorted out and some to sorting out incorrect allocations of dividends (which sometimes happens) ... but generally the closure is just a matter of going over all the old reviews and making final payments and accounts .
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014 http://foggy.blogs.iva.co.uk