Thanks for your reply. I was running it from ArcMap, the tool in ArcToolbox under 3D Analyst Tools, then Conversion, then from File, LAS to Multipoint. I created a new file geodatabase before I ran this function so that the new feature class can be put into the geodatabase. The Lidar_pts was the name I gave to the output feature class. I have tried "lidarpts", "LidarPoints", "Points", ... It didn't make a difference. The input are 20 .las files that have different names. I have attached two screen shots: the user interface with the inputs and output, the other the results window showing the error. I never failed to recreate the problem, regardless of what name I gave to the output feature class. The tool requires a new output feature class. It doesn't accept a feature class that already exist. I have tried to produce a shape file too, it didn't work either.
I don't know what version the geodatabase is. I am running ArcGIS 10.1. Just upgraded from ArcGIS 10.0 about two weeks ago. I did not encounter this problem with ArcGIS 10.0. As for the las file, they chose a strange coordinate system: NAD_1983_BLM_Zone_16N_ftUS. ArcGIS 10.1 didn't recognize that. I had to set it up manually when creating the LAS dataset. For that matter, I tried Point File Information. It reported no error, but didn't generate the file correctly. There was nothing in the file, no record in the attribute table. How could I fix this?
Thank you.