system message 44: Invalid Mixing of account types for setting up a new Depreciation GL account 8001

The existing Description GL account is set up as 8000 with Expense Account Type without "Account Category".

When user adds an additional Depreciation account begins with 2 or 8,  a system message 44 pop up on the screen. However, system takes it if beginning number starts with 7 or 9.  

Would like to know where the system controls the account number set up?

NOTE: the message pops up when user tabs over the Account Category field.

Thanks

Ginny