This error occurs when an invalid attribute(%s) is used inside a modifier like Add, Delete, or Replace(%s).
Use a valid attribute in the modifier.
Example
[#Form:Balance Sheet]
Add: Add: Button:Change Period
The attribute Add is not valid attribute for modifier attribute Add, Hence the message error T0034: Attribute 'Add' is not allowed within the modifier 'Add'.
The code is corrected by removing the attribute Add from the modifier.
[#Form:Balance Sheet]
Add: Button:Change Period