Recurring "read_data" error!

I have been struggling in vain to undo an error occurring when LAMMPS tries to read a data file. It flags “ERROR: No bonds allowed with this atom style”. If I change “atom_style” to another and rerun, it flags “ERROR: Incorrect atom format in data file”. Can someone help to understand this please? Thanks.

When you select a atom_style, you are telling LAMMPS to use a certain data structure for storing the physical information of your system, hence you need to stick to a precise line syntax for the header, atom section, and so on, as explained in the read_data documentation.
It goes without saying that randomly changing the atom style without updating the data file will inevitably produce an error. You need first to understand the physical model used to describe your system, and then chose the right settings for the data file, force field, and simulation parameters.
Seek advice in your group, or find a similar simulation in the examples folder and study the input files carefully. Or at least, describe better what you want to do, explain why you want to do it that way, and provide your input files.