I think you may be experiencing this issue if you're using the cPanel/DirectAdmin/Interworx module. You can resolve it by updating the package to not use a module group, or update the module rows in that group to have a high account limit:
Edit the package you were ordering. Under "Module Options", change the "Server Group" to "Any". -or- Update the module row and change it's "Account Limit" to a large number.
It is a priority for us to include it in the version 4 release, so we can't drop it. It requires several core changes that need to be made anyway, which lets us factor out some code to be deprecated, and simplify the code base. These changes have to be made at some point, and there is a larger benefit to them happening now.