NI Contributions - enquiry letter with CA4098A to fill in

Well the NI Contribs office have written to my one-man company saying there is a discrepancy on my end of year P14 for 2010/11.  They want details of all my salary payments that year, and suggest I might like to enter them onto the CA4098A form that they enclosed.  I've not had experience of such an enquiry before.  I'm thinking I'll send them a copy of my P11 deductions card.  I get my salary quarterly, it is quite likely that I didn't get NI contribs exactly right, but I doubt I've made a huge error.

So is this enquiry likely to develop into something more serious? 

Anyone got any experience with enquiries like this?