3819716 - What's the impact for the account code in existing report if I updated Ledger in user profile?

We created new ledger and update it to some users' profile recently.
However, when processor would like change expense type for one report entry, it pops up missing account code error.
May I know why it happened and what's the impact for the account code in existing report if I updated Ledger in user profile?

Changing a user's ledger in their profile may cause missing account code errors when editing expense types on older reports created under the previous ledger. , KBA , CON-EXP-ADM-ACC , Account Codes , Problem