Hi! If you open an issue on the GitHub of the project, and provide the necessary details in the report, I can look into your problem.
The error you're getting means that the file you're trying to import using the addon is likely not a valid Arma 3 P3D model file (or at least the addon doesn't recognizes it as one).
Tried like 30 .p3d files only script errors :/ I hate to leave bad reviews, will change if it gets updated...Blender 4.3 here, cant select that also in Version drop-down... Python: Traceback (most recent call last): File "C:\Users********\AppData\Roaming\Blender Foundation\Blender\4.3\extensions\blender_org\Arma3ObjectBuilder\ui\import_export_p3d.py", line 101, in execute lod_objects = import_p3d.read_file(self, context, file) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "C:\Users*******\AppData\Roaming\Blender Foundation\Blender\4.3\extensions\blender_org\Arma3ObjectBuilder\io\import_p3d.py", line 432, in read_file mlod = p3d.P3D_MLOD.read(file, operator.first_lod_only) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "C:\Users******\AppData\Roaming\Blender Foundation\Blender\4.3\extensions\blender_org\Arma3ObjectBuilder\io\data_p3d.py", line 778, in read raise P3D_Error("Invalid MLOD signature: %s" % str(signature)) bl_ext.blender_org.Arma3ObjectBuilder.io.data_p3d.P3D_Error: P3D - Invalid MLOD signature: b'clas'