Hi Claudia,
I had a similar issue and found your thread in my search.
My issue was converting multiple LiDAR .LAS files to a single multipoint file (LAS to Multipoint).
I received the following errors:
Error: 999999
FDO error: -1
FDO error:-1 [featureclass_name]
Failed to execute (LAStoMultipoint)
I can't speak to your issue specifically but I just got off of the phone with ESRI support and they told me that my issue is directly related to 10.1 Service Pack1.
I was told that many LiDAR errors are resultant of SP1. I was directed to go to control panel / programs and features / installed updates /
highlight ArcGIS SP1 / right click / remove.
This apparently reverts to 10.1 SP0 and the errors should go away.
Might be worth looking into.