The LAS dataset pyramid distributes LAS points across multiple levels that are organized in an internal tree structure. The maximum number of levels available for this tree structure is defined by the type of integer used to store the node ID. Currently, this is a 64-bit integer, which has a maximum limit of 264. While this limit is sufficient for most use cases, a LAS dataset containing very dense points covering a large area may encounter this limit and return the error. In some cases, this may be caused by the presence of densely sampled points in small areas. This can happen when the lidar sensor idles in a particular location while it is collecting data. You can evaluate the point density of a LAS dataset using the LAS Point Statistics As Raster tool with the Method parameter set to Point Count.
You can either divide the source files between multiple LAS datasets or use the Thin LAS tool to create .las files with coarser point density that can be loaded in one LAS dataset.