For the Currency Defaults of a Company record in the InterCompany Plug-In, the default Analysis Codes used for the Exchange Differences need to be of type Discount Analysis.
So you either need to select a different Analysis Code that is a Discount Analysis type, create a new Analysis Code of the correct type, or you need to change the type of the one you are trying to use.
For details on how to create new Analysis Codes see this article for Sales Ledger or this article for Purchase Ledger.
To change the type of an existing Analysis Code, follow the instructions below.
These instructions assume it is a new Analysis code that has not yet been used. This describes the process for a Sales Ledger Analysis Code, but the process is the same for a Purchase Ledger Analysis Code except you select the Purchase Ledger/Creditors module at the start instead.
Ribbon style menu:
Select Debtors from the main menu
Select Analysis
Find the Analysis Code you wish to edit
Click Edit
Click on red Sales Analysis button (or Purch Analysis if in the Purchase Ledger) to change the type to Discount Analysis
Click Save
You should now be able to return to the InterCompany Plug-In options to complete the setup of the currency Defaults