I am new to LAMMPS and have been working my way through available examples before diving into my own research using LAAMPS. I am currently working through the tutorial given here: https://avogadro.cc/docs/extensions/lammps-input-for-water/ . I see that this question has been asked here before, but the post was abandoned by the user so there was no indication as to whether or not they sorted out their problem, and if so how. There was also a post on an Avogadro forum that asked the same question, but there were no responses given.
I am having the same issue as this other user. That is, I am able to get to the point where I have to save the structure file in a LAMMPS readable format, but my computer tells me that water.lmpdat is not a valid file name. Saving the .lmp file did work, but this is the input script and not the coordinate data file for the water box.
For reference, I am running Windows 10, and have Avogadro version 1.2.0 installed onto my computer. I have tried using other file extensions like .dat, .data, .in, and .input and I am given the same "File name is not valid error". I have also tried independently generating the coordinate data file and am met with formatting errors, so I would like to try this approach again to see if it works this time. Any insight on this matter is welcome, and if there is any other information I should provide, let me know in a reply/comment and I will provide what I can.