Hi Marcel
Thank you for your suggestion re. module account limit. I tried doing that - i.e. setting the Account Limit in Edit cPanel Server to 200. Then in the Module Options in Update Package I set the Server Group back from 'Any' to the group I created and called 'UK', and tested as a client buying a package from that group and it worked just fine, no more "An internal error occurred. The module row is unavailable."! So thank you very much! I don't know why it worked but it did.