# MD: cannot run LAMMPS after installing a new version of DeePMD-kit
This typically happens when you install a new version of DeePMD-kit and copy directly the generated `USER-DEEPMD` to a LAMMPS source code folder and re-install LAMMPS.

To solve this problem, it suffices to first remove `USER-DEEPMD` from LAMMPS source code by 
```bash
make no-user-deepmd
```
and then install the new `USER-DEEPMD`.

If this does not solve your problem, try to decompress the LAMMPS source tarball and install LAMMPS from scratch again, which typically should be very fast.