If there is more than one device in programming mode then it is not possible to program Individual Addresses within that line.
Use the ETS diagnostics function 'Programming Mode' in order to check which device or devices is/are in programming mode.
Use the ETS diagnostics function 'Individual Address Check' in order to switch off the programming mode of the devices that should not be in programming mode.
Please note however, that this will not work either if more than one of these devices have the same Individual Address, this is considered being a topology mistake.