Thanks for your reply. Things have moved on and, because of this and other problems I'm going to have to revert to the original server.
I don't understand why but I suspect that this is being caused by some sort of clash using perl5.10.1 and perl5.22.0 modules (that or some inconsistency with underlying apps that the modules rely on).
Once I've reverted to the old system I'll re-install the whole operating system on the new server and see if that fixes the problem.