I'm confused, you state you sold the "book of buisness", I presume your goodwill and client list at the time, yet the company was insolvent. What happened the revenue from that sale, did you use it to pay off other creditors and were they preferential creditors over BoI or did you just take the money any walk away?. Did you go through a proper insolvency process.?
Risk here is not any guarantee, risk is that you, as a company director, could be held personally liable.