When creating a new ticket and try to associate it to a parent and then save the changes, the following error message might appear:

"Error- AHD05999:Parent ticket type is not same as current ticket type"

In addition, when creating a new ticket by copying the ticket from "Copy" option in the ticket's menu, and then setting the parent ticket, the following message might appear:
 
"Error 1 attempting to set parent to "cr:XXXXXXX": No message available"

The product behavior was changed to not allow any type of relationship. Out of the box it can associate child incidents to a request (by creating them from the request itself), but it cannot manually create the relationship or reverse it.

CA Service Desk Manager (CA SDM) 14.1 cum4 / 17.x

A NX.env value was introduced to the product in later releases to allow revert it to the older behavior.
Add '@NX_TICKET_REL=Yes' to NX.env and NX.env_nt.tpl files using below commands:

pdm_options_mgr -c -s TICKET_REL -v Yes -a pdm_option.inst
pdm_options_mgr -c -s TICKET_REL -v Yes -a pdm_option.inst -t

Notes:

• This will need to be done to all SDM servers in case of Conventional mode having secondary servers or Advanced Availability mode.
• In order to avoid losing the changes when running pdm_configure command, it is required to add it to NX.env_nt.tpl file as well using the -t option.
• Instead of adding  the NX_TICKET_REL directly to the NX env files, it is recommended to run the commands from command prompt to add them.
• Update children cannot be used for cross ticket relationships. This has to be done only through Parent field, manually, for every ticket.