I've encountered an error while trying to make an account that belongs to a net account Non Reconcilable.

If an account should no longer be reconcilable, the attribute for reconcilability should be removed.  However, this is not quite as simple if that account belongs to a Net Account.

In order to update the reconcilable attribute for an account that is part of a Net Account, it must first be removed from the Net Account to which it belongs.  To do that, the Net Account must not have had work begun on it.  Once it's confirmed that it's not been started, go to Accounts > Create/Update Net Accounts and use the drop down arrow to select the Net Account that should be updated with the account removal.

ART will open the parameters for the Net Account and you will be able to select the account to be removed by checking the checkbox to left of it.  Then click the button to 'Remove Account'

ART will prompt you to be sure that the account should be removed.  Select 'OK'.

Now that the account to be made irreconcilable has been removed from the Net Account, the attribute change can be made. Go to Accounts > Account Mass/Bulk Update

Search for the account using the search parameters and ART will pull back any applicable accounts.  To select the one(s) to be changed, check the checkbox(es) to the left of the account(s), remove the check mark from the 'Reconcilable' attribute and click 'Save'.