Please understand that setting the main bank fields "Bank key" (BANKL) and "Bank Account no." (BANKN) to READ-ONLY makes no real sense as it prevents the user from changing his bank data.
Now, if the user changes his bank account from Bank A to Bank B he can not enter this data in ESS. For that reason, kindly remove the READ-ONLY settings from table T588MFPROPC for these 2 fields.
Furthermore, if you really want to have these 2 fields shown as READ-ONLY you should rather use an implementation of the BADI HRPAD00INFTYUI to set the visibility to READ-ONLY. If you are using T588MFPROPC to set these fields to READ-ONLY this means that also the content of these 2 fields will be re-set to its initial value. check class CL_HRPA_MASTERDATA_BL' You can check via PUI_IT For that reason, I highly recommend to use BADI HRPAD00INFTYUI to set these fields as READ-ONLY.