Most likely, the client is not on a security matrix for BDMS. They will need to contact the maintainer of the security matrix for the application which they are trying to access. See knowledge article BDM: How to request access for the current list of category owners.
The BDM Administrator will add the appropriate permissions after receiving an updated security matrix via a Katalyst service request. The permissions sometimes do not take effect immediately, as they must propagate through the system.