As I understand company law (although not a lawyer, I have been running a Ltd company for 19 years), you cannot just transfer assets between companies, they have to be valued and sold at a fair market rate. Depending on the circustances, undervaluing assets in order to sell them cheaply to another company (whether you own it or not) may come under the heading of tax evasion, which is illegal, or fraud, if it is in order to remove them from the reach of creditors.

But it would all depend who values them. I imagine there is some uncertainty in the value of a copyright. I can imagine an arguement running as follows 'We haven't sold any for x years, therefore the copyright is worthless'.