The Accounts dimension is different than any other dimension when it comes to adding roll up accounts. Accounts can hold data, so by default they system will not let you move existing accounts under an account, even if it is new, because the system would not know what to do with any data that might exist in the account you are trying to make a parent. Because of this reason, there is a trick to making a new account eligible to be a roll up account, first you have to give it 1 new child account (adding a new account below an existing account will move all of the existing accounts data to the new child), once the account has 1 child account, you are then free to move other accounts under it.
This example will create a new roll up account for 6100 Payroll and 6200 Taxes and Benefits called “Payroll & Taxes” using the account setup below.
Step 1: Add the new “Payroll & Taxes” account below 6000 Operating Expense (re order it as necessary).
Step 2: Add a new temporary account to the new “Payroll & Taxes” account, you will be deleting the account so nothing about it matters.
Step 3: Now you can either drag and drop the existing accounts under “Payroll & Taxes” or change the Rolls Up to property in the Account Details section to the right. You will need to click through the dialogs letting you know that changing account structure affects even locked versions.
Step 4: Delete the “temp” account created in Step 2.