Party Merge Error (R12.1.3)

Hi All,

We are trying to merge two parties and receiving the following error:

The following parties cannot be merged because they belong to separate hierarchies. Please remove the hierarchy relationship for one or more of the parties or have your administrator allow parties to participate in multiple hierarchies. Parties: 520129, 171465

The surviving party is 171465 and party getting merged is 520129.

Party 520129 has a parent party which does not match with the parent party of 171465, is this the reason for this error, if so what is the solution:

1> merge the parent parties first

2> inactivate the parent child relationship for party 520129 - if this is the solution, please provide the steps.